Synovial sarcoma is a highly malignant tumor which arises from synovial tissue derived from mesothelium and its occurrence is very rare. Furthermore, congenital synovial sarcoma which developed from aggressive deposition of tumor cells during intra-uterine fetal life is extremely rare. Authors present a case of congenital synovial sarcoma which is found in the right ankle of one month old boy, because of its rarity of occurrence.