It is difficult to repair the pulp defect of finger with good function. Here reported two cases of pulp defect of the thumb which were repaired with free palmris brevis musculo-cutaneous flap. The flap was designed as the following: taken the line crossing the pisiform and metacarpo-phalangeal joint of the little finger as the longitudinal axis of the flap. The proximal end of the flap was at the level of pisiform and the distal end was the distal transverse palmar crease. The radial border was the radial side of the palmris brevis and ulnar border was the ulnar edge of the palm. The flap should not be larger than 6.5 cm x 2.5 cm. The flap was dissected with proper ulnar vessels and the accompanying arterial branch and superficial branch of the ulnar nerve. The flap was transferred to repair the pulp defect of the thumb. The vessels were anastomosed with the radial artery and cephalic vein at the snuffbox. The nerves were sutured to the digital nerve. Three months after operation, the defect was healed and the sensation of pulp was recovered. The donor area was painless and without sensation disturbance. The motion of the little finger was normal. The function of the thumb was restored. It was concluded that the palmaris brevis musculocutaneous flap is one of the best donor region to repair pulp defect of thumb.