Objective To investigate the effectiveness of the terminal extensor tendon reconstrution by palmaris longus tendon graft for the treatment of old mallet finger deformity. Methods Between February 2009 and February 2011, 32 patients with old mallet finger deformity were treated with palmaris longus tendon graft. There were 28 males and 4 females with an average age of 32.5 years (range, 22-58 years). The injury causes included sports injury in 26 cases and punctured injury in 6 cases. The index finger was involved in 8 cases, the middle finger in 3 cases, the ring finger in 16 cases, and the little finger in 5 cases. According to the Rockwell’s classification, all patients were classified as type I. The time from injury to operation was 4-16 weeks (mean, 6 weeks). Results Primary healing was obtained in all incisions; no necrosis, infection, or nail bed injury occurred. All patients were followed up 12-20 months (mean, 14 months). The patients had no pain or paresthesia of volar finger. According to Patel’s functional assessment system, the results were excellent in 8 cases, good in 21 cases, fair in 2 cases, and poor in 1 case at last follow-up, with an excellent and good rate of 90.6%. Conclusion Reconstruction of the terminal extensor tendon by palmaris longus tendon graft is a reliable method to treat old mallet finger deformity.