Objective:To explore the clinical effect of keystone flap (KF) on repair of soft tissue defects at the donor site after flap transfer.Methods:From October 2020 to December 2022, in the Department of Microsurgical Rapair of First Affiliated Hospital of Xinjiang Medical University, 12 patients were repaired with KF after transfer of flaps. There were 3 donor sites for lateral thigh myocutaneous flap, 3 for sural nerve nutrient vascular flap, 4 for latissimus dorsi myocutaneous flap and 2 for medial supramalleolar island flap. Size of the KF was 15.0 cm × 12.0 cm-30.0 cm × 20.0 cm. Types of KF were: 3 of type I, 5 of type IIA, 2 of type IIB and 2 of type Sydney Melanoma Unit (SMU) modification KF design. Four patients were reviewed by telephone follow-up, 5 by WeChat and 3 with outpatient clinic visits to observe the appearance of the transferred KF and postoperative complications. Appearance of flaps was scored and analysed using Vancouver Scar Scale (VSS) and Scar Cosmesis Assessment and Rating (SCAR) .Results:The average follow-up period was 15.9 (2-27) months. The colour and texture of the transferred KF were similar to that of the surrounding skin, together with good sensation recovery. No complication such as osteofascial compartment syndrome, necrosis, wound dehiscence and venous congestion occurred in all patients. At the final follow-up, the scores for VSS was 2.17±0.58 and the score for SCAR was 5.33±1.23, with satisfactory repairing outcomes.Conclusion:As a relay flap, the KF is a simple and effective flap for reconstruction of the defects at the donor site and it can avoid complications that can be caused by direct closure of the soft tissue defect or a wound dehiscence after skin grafting.