diff --git a/bson/bson.go b/bson/bson.go
index 7fb7f8cae..17f6055d2 100644
--- a/bson/bson.go
+++ b/bson/bson.go
@@ -257,10 +257,22 @@ func NewObjectIdWithTime(t time.Time) ObjectId {
 	return ObjectId(string(b[:]))
 }
 
+// objectIdStringer contains the function used in String() method of ObjectId type.
+// It can be set by user through the exported SetIdStringer function.
+var objectIdStringer = func(id ObjectId) string {
+	return fmt.Sprintf(`ObjectIdHex("%x")`, string(id)) // id default stringer
+}
+
+// SetIdStringer defines how the string representation of ObjectId type should be in its String() method.
+func SetIdStringer(f func(ObjectId) string) {
+	objectIdStringer = f
+}
+
 // String returns a hex string representation of the id.
-// Example: ObjectIdHex("4d88e15b60f486e428412dc9").
+// The default representation looks like: ObjectIdHex("4d88e15b60f486e428412dc9"),
+// which can be changed/defined through the function argument provided for SetIdStringer.
 func (id ObjectId) String() string {
-	return fmt.Sprintf(`ObjectIdHex("%x")`, string(id))
+	return objectIdStringer(id)
 }
 
 // Hex returns a hex representation of the ObjectId.
@@ -279,7 +291,7 @@ var nullBytes = []byte("null")
 func (id *ObjectId) UnmarshalJSON(data []byte) error {
 	if len(data) > 0 && (data[0] == '{' || data[0] == 'O') {
 		var v struct {
-			Id json.RawMessage `json:"$oid"`
+			Id   json.RawMessage `json:"$oid"`
 			Func struct {
 				Id json.RawMessage
 			} `json:"$oidFunc"`