diff -r d428b4ee8b39 Lib/json/encoder.py
--- a/Lib/json/encoder.py	Fri Jan 09 16:00:30 2015 +0100
+++ b/Lib/json/encoder.py	Sun Jan 11 06:06:13 2015 +0900
@@ -7,6 +7,10 @@
 except ImportError:
     c_encode_basestring_ascii = None
 try:
+    from _json import encode_basestring as c_encode_basestring
+except ImportError:
+    c_encode_basestring = None
+try:
     from _json import make_encoder as c_make_encoder
 except ImportError:
     c_make_encoder = None
@@ -30,7 +34,7 @@
 INFINITY = float('inf')
 FLOAT_REPR = repr
 
-def encode_basestring(s):
+def py_encode_basestring(s):
     """Return a JSON representation of a Python string
 
     """
@@ -39,6 +43,9 @@
     return '"' + ESCAPE.sub(replace, s) + '"'
 
 
+encode_basestring = (c_encode_basestring or py_encode_basestring)
+
+
 def py_encode_basestring_ascii(s):
     """Return an ASCII-only JSON representation of a Python string
 
diff -r d428b4ee8b39 Lib/test/test_json/test_encode_basestring.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Lib/test/test_json/test_encode_basestring.py	Sun Jan 11 06:06:13 2015 +0900
@@ -0,0 +1,44 @@
+from collections import OrderedDict
+from test.test_json import PyTest, CTest
+
+
+CASES = [
+    # Left side is Copied from test_encode_basestring_ascii
+    ('/\\"\ucafe\ubabe\uab98\ufcde\ubcda\uef4a\x08\x0c\n\r\t`1~!@#$%^&*()_+-=[]{}|;:\',./<>?', '"/\\\\\\"\ucafe\ubabe\uab98\ufcde\ubcda\uef4a\\b\\f\\n\\r\\t`1~!@#$%^&*()_+-=[]{}|;:\',./<>?"'),
+    ('\u0123\u4567\u89ab\ucdef\uabcd\uef4a', '"\u0123\u4567\u89ab\ucdef\uabcd\uef4a"'),
+    ('controls', '"controls"'),
+    ('\x08\x0c\n\r\t', '"\\b\\f\\n\\r\\t"'),
+    ('{"object with 1 member":["array with 1 element"]}', '"{\\"object with 1 member\\":[\\"array with 1 element\\"]}"'),
+    (' s p a c e d ', '" s p a c e d "'),
+    ('\U0001d120', '"\U0001d120"'),
+    ('\u03b1\u03a9', '"\u03b1\u03a9"'),
+    ("`1~!@#$%^&*()_+-={':[,]}|;.</>?", '"`1~!@#$%^&*()_+-={\':[,]}|;.</>?"'),
+    ('\x08\x0c\n\r\t', '"\\b\\f\\n\\r\\t"'),
+    ('\u0123\u4567\u89ab\ucdef\uabcd\uef4a', '"\u0123\u4567\u89ab\ucdef\uabcd\uef4a"'),
+    # Edge cases
+    ('\u0000\u001f\u007f\u0080\uffff\U00010000\U0010ffff', '"\\u0000\\u001f\x7f\u0080\uffff\U00010000\U0010ffff"'),
+]
+
+class TestEncodeBasestring:
+    def test_encode_basestring(self):
+        fname = self.json.encoder.encode_basestring.__name__
+        for input_string, expect in CASES:
+            result = self.json.encoder.encode_basestring(input_string)
+            self.assertEqual(result, expect,
+                '{0!r} != {1!r} for {2}({3!r})'.format(
+                    result, expect, fname, input_string))
+
+    def test_ordered_dict(self):
+        # See issue 6105
+        items = [('one', 1), ('two', 2), ('three', 3), ('four', 4), ('five', 5)]
+        s = self.dumps(OrderedDict(items), ensure_ascii=False)
+        self.assertEqual(s, '{"one": 1, "two": 2, "three": 3, "four": 4, "five": 5}')
+
+    def test_sorted_dict(self):
+        items = [('one', 1), ('two', 2), ('three', 3), ('four', 4), ('five', 5)]
+        s = self.dumps(dict(items), sort_keys=True, ensure_ascii=False)
+        self.assertEqual(s, '{"five": 5, "four": 4, "one": 1, "three": 3, "two": 2}')
+
+
+class TestPyEncodeBasestring(TestEncodeBasestring, PyTest): pass
+class TestCEncodeBasestring(TestEncodeBasestring, CTest): pass
diff -r d428b4ee8b39 Lib/test/test_json/test_encode_basestring_ascii.py
--- a/Lib/test/test_json/test_encode_basestring_ascii.py	Fri Jan 09 16:00:30 2015 +0100
+++ b/Lib/test/test_json/test_encode_basestring_ascii.py	Sun Jan 11 06:06:13 2015 +0900
@@ -11,9 +11,6 @@
     (' s p a c e d ', '" s p a c e d "'),
     ('\U0001d120', '"\\ud834\\udd20"'),
     ('\u03b1\u03a9', '"\\u03b1\\u03a9"'),
-    ('\u03b1\u03a9', '"\\u03b1\\u03a9"'),
-    ('\u03b1\u03a9', '"\\u03b1\\u03a9"'),
-    ('\u03b1\u03a9', '"\\u03b1\\u03a9"'),
     ("`1~!@#$%^&*()_+-={':[,]}|;.</>?", '"`1~!@#$%^&*()_+-={\':[,]}|;.</>?"'),
     ('\x08\x0c\n\r\t', '"\\b\\f\\n\\r\\t"'),
     ('\u0123\u4567\u89ab\ucdef\uabcd\uef4a', '"\\u0123\\u4567\\u89ab\\ucdef\\uabcd\\uef4a"'),
diff -r d428b4ee8b39 Modules/_json.c
--- a/Modules/_json.c	Fri Jan 09 16:00:30 2015 +0100
+++ b/Modules/_json.c	Sun Jan 11 06:06:13 2015 +0900
@@ -47,7 +47,7 @@
     PyObject *item_separator;
     PyObject *sort_keys;
     PyObject *skipkeys;
-    int fast_encode;
+    PyCFunction fast_encode;
     int allow_nan;
 } PyEncoderObject;
 
@@ -218,6 +218,97 @@
     return rval;
 }
 
+static PyObject *
+escape_unicode(PyObject *pystr)
+{
+    /* Take a PyUnicode pystr and return a new escaped PyUnicode */
+    Py_ssize_t i;
+    Py_ssize_t input_chars;
+    Py_ssize_t output_size;
+    Py_ssize_t chars;
+    PyObject *rval;
+    void *input;
+    int kind;
+    Py_UCS4 maxchar;
+
+    if (PyUnicode_READY(pystr) == -1)
+        return NULL;
+
+    maxchar = PyUnicode_MAX_CHAR_VALUE(pystr);
+    input_chars = PyUnicode_GET_LENGTH(pystr);
+    input = PyUnicode_DATA(pystr);
+    kind = PyUnicode_KIND(pystr);
+
+    /* Compute the output size */
+    for (i = 0, output_size = 2; i < input_chars; i++) {
+        Py_UCS4 c = PyUnicode_READ(kind, input, i);
+        switch (c) {
+        case '\\': case '"': case '\b': case '\f':
+        case '\n': case '\r': case '\t':
+            output_size += 2;
+            break;
+        default:
+            if (c <= 0x1f)
+                output_size += 6;
+            else
+                output_size++;
+        }
+    }
+
+    rval = PyUnicode_New(output_size, maxchar);
+    if (rval == NULL)
+        return NULL;
+
+    kind = PyUnicode_KIND(rval);
+
+#define ENCODE_OUTPUT do { \
+        chars = 0; \
+        output[chars++] = '"'; \
+        for (i = 0; i < input_chars; i++) { \
+            Py_UCS4 c = PyUnicode_READ(kind, input, i); \
+            switch (c) { \
+            case '\\': output[chars++] = '\\'; output[chars++] = c; break; \
+            case '"':  output[chars++] = '\\'; output[chars++] = c; break; \
+            case '\b': output[chars++] = '\\'; output[chars++] = 'b'; break; \
+            case '\f': output[chars++] = '\\'; output[chars++] = 'f'; break; \
+            case '\n': output[chars++] = '\\'; output[chars++] = 'n'; break; \
+            case '\r': output[chars++] = '\\'; output[chars++] = 'r'; break; \
+            case '\t': output[chars++] = '\\'; output[chars++] = 't'; break; \
+            default: \
+                if (c <= 0x1f) { \
+                    output[chars++] = '\\'; \
+                    output[chars++] = 'u'; \
+                    output[chars++] = '0'; \
+                    output[chars++] = '0'; \
+                    output[chars++] = Py_hexdigits[(c >> 4) & 0xf]; \
+                    output[chars++] = Py_hexdigits[(c     ) & 0xf]; \
+                } else { \
+                    output[chars++] = c; \
+                } \
+            } \
+        } \
+        output[chars++] = '"'; \
+    } while (0)
+
+    if (kind == PyUnicode_1BYTE_KIND) {
+        Py_UCS1 *output = PyUnicode_1BYTE_DATA(rval);
+        ENCODE_OUTPUT;
+    } else if (kind == PyUnicode_2BYTE_KIND) {
+        Py_UCS2 *output = PyUnicode_2BYTE_DATA(rval);
+        ENCODE_OUTPUT;
+    } else {
+        Py_UCS4 *output = PyUnicode_4BYTE_DATA(rval);
+        assert(kind == PyUnicode_4BYTE_DATA);
+        ENCODE_OUTPUT;
+    }
+#undef ENCODE_OUTPUT
+
+#ifdef Py_DEBUG
+    assert(_PyUnicode_CheckConsistency(rval, 1));
+#endif
+    return rval;
+}
+
 static void
 raise_errmsg(char *msg, PyObject *s, Py_ssize_t end)
 {
@@ -530,6 +621,31 @@
     return rval;
 }
 
+
+PyDoc_STRVAR(pydoc_encode_basestring,
+    "encode_basestring(string) -> string\n"
+    "\n"
+    "Return a JSON representation of a Python string"
+);
+
+static PyObject *
+py_encode_basestring(PyObject* self UNUSED, PyObject *pystr)
+{
+    PyObject *rval;
+    /* Return a JSON representation of a Python string */
+    /* METH_O */
+    if (PyUnicode_Check(pystr)) {
+        rval = escape_unicode(pystr);
+    }
+    else {
+        PyErr_Format(PyExc_TypeError,
+                     "first argument must be a string, not %.80s",
+                     Py_TYPE(pystr)->tp_name);
+        return NULL;
+    }
+    return rval;
+}
+
 static void
 scanner_dealloc(PyObject *self)
 {
@@ -1223,7 +1339,14 @@
     s->item_separator = item_separator;
     s->sort_keys = sort_keys;
     s->skipkeys = skipkeys;
-    s->fast_encode = (PyCFunction_Check(s->encoder) && PyCFunction_GetFunction(s->encoder) == (PyCFunction)py_encode_basestring_ascii);
+    s->fast_encode = NULL;
+    if (PyCFunction_Check(s->encoder)) {
+        PyCFunction f = PyCFunction_GetFunction(s->encoder);
+        if (f == (PyCFunction)py_encode_basestring_ascii ||
+                f == (PyCFunction)py_encode_basestring) {
+            s->fast_encode = f;
+        }
+    }
     s->allow_nan = PyObject_IsTrue(allow_nan);
 
     Py_INCREF(s->markers);
@@ -1372,7 +1495,7 @@
 {
     /* Return the JSON representation of a string */
     if (s->fast_encode)
-        return py_encode_basestring_ascii(NULL, obj);
+        return s->fast_encode(NULL, obj);
     else
         return PyObject_CallFunctionObjArgs(s->encoder, obj, NULL);
 }
@@ -1840,6 +1963,10 @@
         (PyCFunction)py_encode_basestring_ascii,
         METH_O,
         pydoc_encode_basestring_ascii},
+    {"encode_basestring",
+        (PyCFunction)py_encode_basestring,
+        METH_O,
+        pydoc_encode_basestring},
     {"scanstring",
         (PyCFunction)py_scanstring,
         METH_VARARGS,