OBJECTIVE To investigate the compression factor and clinical manifestation of the compression of deep branch of the ulnar nerve at the wrist. METHODS Anatomic study was done on both sides of 10 cadavers, the deep branch of ulnar nerve, the Guyon’s canal and the flexor digiti minimi brevis pedis were observed. Then from Jan. 1990 to Jan. 1997, 5 patients with compression of the deep branch of ulnar nerve at the wrist were treated clinically. Among them, there were 4 males and 1 female, aged from 37 to 48 years and the course of disease ranged from 1 to 5 months. RESULTS The motor branch of the ulnar nerve passed under the tendinous arcade of flexor digiti minimi brevis pedis. Occasionally, the branch of ulnar artery overpassed the motor branch. Clinically, the tendinous arcade compressed the motor branch was released, and after 2 to 4 years follow-up, the clinical results were satisfactory. CONCLUSION The main compression factor of the ulnar nerve at the wrist is the tendinous arcade of the flexor digiti minimi brevis pedis, the tendinous arcade should be released sufficiently during the operation.