diff --git a/asv_bench/benchmarks/io/json.py b/asv_bench/benchmarks/io/json.py
index bb09fe0ff634d..39f234c6fa816 100644
--- a/asv_bench/benchmarks/io/json.py
+++ b/asv_bench/benchmarks/io/json.py
@@ -294,7 +294,8 @@ def time_float_longint_str_lines(self):
 class ToJSONMem:
     def setup_cache(self):
         df = DataFrame([[1]])
-        frames = {"int": df, "float": df.astype(float)}
+        df2 = DataFrame(range(8), date_range("1/1/2000", periods=8, freq="T"))
+        frames = {"int": df, "float": df.astype(float), "datetime": df2}
 
         return frames
 
@@ -308,5 +309,10 @@ def peakmem_float(self, frames):
         for _ in range(100_000):
             df.to_json()
 
+    def peakmem_time(self, frames):
+        df = frames["datetime"]
+        for _ in range(10_000):
+            df.to_json(orient="table")
+
 
 from ..pandas_vb_common import setup  # noqa: F401 isort:skip
diff --git a/doc/source/whatsnew/v2.0.0.rst b/doc/source/whatsnew/v2.0.0.rst
index abe5a4840d57f..ca50bf46efd22 100644
--- a/doc/source/whatsnew/v2.0.0.rst
+++ b/doc/source/whatsnew/v2.0.0.rst
@@ -870,6 +870,7 @@ Performance improvements
 - Performance improvement in :func:`read_csv` when passing :func:`to_datetime` lambda-function to ``date_parser`` and inputs have mixed timezone offsetes (:issue:`35296`)
 - Performance improvement in :meth:`.SeriesGroupBy.value_counts` with categorical dtype (:issue:`46202`)
 - Fixed a reference leak in :func:`read_hdf` (:issue:`37441`)
+- Fixed a memory leak in :meth:`DataFrame.to_json` and :meth:`Series.to_json` when serializing datetimes and timedeltas (:issue:`40443`)
 
 .. ---------------------------------------------------------------------------
 .. _whatsnew_200.bug_fixes:
diff --git a/pandas/_libs/src/ujson/python/objToJSON.c b/pandas/_libs/src/ujson/python/objToJSON.c
index a6f18e0aec4d9..13b96f9f8fccd 100644
--- a/pandas/_libs/src/ujson/python/objToJSON.c
+++ b/pandas/_libs/src/ujson/python/objToJSON.c
@@ -350,13 +350,15 @@ static char *PyUnicodeToUTF8(JSOBJ _obj, JSONTypeContext *tc,
 static char *NpyDateTimeToIsoCallback(JSOBJ Py_UNUSED(unused),
                                       JSONTypeContext *tc, size_t *len) {
     NPY_DATETIMEUNIT base = ((PyObjectEncoder *)tc->encoder)->datetimeUnit;
-    return int64ToIso(GET_TC(tc)->longValue, base, len);
+    GET_TC(tc)->cStr = int64ToIso(GET_TC(tc)->longValue, base, len);
+    return GET_TC(tc)->cStr;
 }
 
 /* JSON callback. returns a char* and mutates the pointer to *len */
 static char *NpyTimeDeltaToIsoCallback(JSOBJ Py_UNUSED(unused),
                                        JSONTypeContext *tc, size_t *len) {
-    return int64ToIsoDuration(GET_TC(tc)->longValue, len);
+    GET_TC(tc)->cStr = int64ToIsoDuration(GET_TC(tc)->longValue, len);
+    return GET_TC(tc)->cStr;
 }
 
 /* JSON callback */