An unusual congenital anomaly of the thumb had been seen in one patient. It consisted of skeletal hypoplasia having short and slender metacarpal, abducted and extended thumb, malposition and abnormal insertion of flexor pollucis longus, and absence of thenar muscle. Surgical reconstruction have two steps. At first operation, the abnormal insertion of flexor pollucis longus was corrected into the normal course of long flexor, then it's insertion site changed from the base of the proximal phalanx to the base of the distal phalanx. Thereafter, at second operation, the 4th flexor digitorum superficialis tendon transferred to the thumb followed to restore lost opposition due to absence of intrinsic thenar muscle, After these operation, the period of the follow-up was 13 months. The patient could have the useful grasp and pinch, but there was no improvement in cosmetic aspect.