diff --git a/py/objstr.c b/py/objstr.c
index c30da00d71..fc9dfd200b 100644
--- a/py/objstr.c
+++ b/py/objstr.c
@@ -408,12 +408,76 @@ mp_obj_t str_format(uint n_args, const mp_obj_t *args) {
     return s;
 }
 
+mp_obj_t str_replace(uint n_args, const mp_obj_t *args) {
+    assert(MP_OBJ_IS_STR(args[0]));
+    assert(MP_OBJ_IS_STR(args[1]));
+    assert(MP_OBJ_IS_STR(args[2]));
+
+    int max_rep = 0;
+    if (n_args == 4) {
+	assert(MP_OBJ_IS_SMALL_INT(args[3]));
+	max_rep = MP_OBJ_SMALL_INT_VALUE(args[3]);
+	if (max_rep == 0) {
+	    return(args[0]);
+	}
+	else if (max_rep < 0) {
+	    max_rep = 0;
+	}
+    }
+    //if max_rep is still 0 by this point we will need to do all possible replacements
+
+    GET_STR_DATA_LEN(args[0], str, str_len);
+    GET_STR_DATA_LEN(args[1], old, old_len);
+    GET_STR_DATA_LEN(args[2], new, new_len);
+    if (old_len > str_len) {
+	return(args[0]);
+    }
+
+    size_t required_len = 0;
+    const byte *old_occurrence;
+    const byte *offset_ptr = str;
+    size_t offset_num = 0;
+    while((old_occurrence = find_subbytes(offset_ptr, str_len - offset_num, old, old_len)) != NULL){
+	required_len += old_occurrence - offset_ptr;
+	required_len += new_len;
+	offset_ptr = old_occurrence + old_len;
+	offset_num = offset_ptr - str;
+    }
+    required_len += str_len - offset_num;
+    byte *data;
+    mp_obj_t replaced_str = mp_obj_str_builder_start(mp_obj_get_type(args[0]), required_len, &data);
+
+    size_t replaced_str_index = 0;
+    int replacements_done = 0;
+    offset_ptr = str;
+    offset_num = 0;
+    while((old_occurrence = find_subbytes(offset_ptr, str_len - offset_num, old, old_len)) != NULL){
+	//copy from just after end of last occurrence of to-be-replaced string to right before start of next occurrence
+    	memcpy(data + replaced_str_index, offset_ptr, old_occurrence - offset_ptr);
+    	replaced_str_index += old_occurrence - offset_ptr;
+	//copy the replacement string
+    	memcpy(data + replaced_str_index, new, new_len);
+    	replaced_str_index += new_len;
+	offset_ptr = old_occurrence + old_len;
+	offset_num = offset_ptr - str;
+
+	replacements_done++;
+	if (max_rep != 0 && replacements_done == max_rep){
+	    break;
+	}
+    }
+    //copy from just after end of last occurrence of to-be-replaced string to end of old string
+    memcpy(data + replaced_str_index, offset_ptr, str_len - offset_num);
+    return mp_obj_str_builder_end(replaced_str);
+}
+
 static MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(str_find_obj, 2, 4, str_find);
 static MP_DEFINE_CONST_FUN_OBJ_2(str_join_obj, str_join);
 static MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(str_split_obj, 1, 3, str_split);
 static MP_DEFINE_CONST_FUN_OBJ_2(str_startswith_obj, str_startswith);
 static MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(str_strip_obj, 1, 2, str_strip);
 static MP_DEFINE_CONST_FUN_OBJ_VAR(str_format_obj, 1, str_format);
+static MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(str_replace_obj, 3, 4, str_replace);
 
 static const mp_method_t str_type_methods[] = {
     { "find", &str_find_obj },
@@ -422,6 +486,7 @@ static const mp_method_t str_type_methods[] = {
     { "startswith", &str_startswith_obj },
     { "strip", &str_strip_obj },
     { "format", &str_format_obj },
+    { "replace", &str_replace_obj },
     { NULL, NULL }, // end-of-list sentinel
 };
 
diff --git a/tests/basics/string_replace.py b/tests/basics/string_replace.py
new file mode 100644
index 0000000000..a1d0f973bb
--- /dev/null
+++ b/tests/basics/string_replace.py
@@ -0,0 +1,8 @@
+print("".replace("a", "b"))
+print("aaa".replace("a", "b", 0))
+print("aaa".replace("a", "b", -5))
+print("asdfasdf".replace("a", "b"))
+print("aabbaabbaabbaa".replace("aa", "cc", 3))
+print("a".replace("aa", "bb"))
+print("testingtesting".replace("ing", ""))
+print("testINGtesting".replace("ing", "ING!"))