We reviewed 10 cases of the ulnar nerve neuropathy at the Guyons canal. The causes can be divided in two groups, one is compression by mass and the other is adhesion by post- operation or trauma. The 6 cases were caused by compression (one ganglion, one schwannoma, one lipoma, one anomalous muscle, one anomalous vessel loop, and one foreign body), 3 cases were by adhesion (one pisiform dislocation, ane wrist fracture, one post operative scar farmation), and the other one case was unknown. There was correlation between the location of mass and the clinical motor or sensory type ulnar neuropathy symptom. Preoperative careful physical examination, electromyogram and radiological study can be helpful to know the causes and location of mass. But in case of unknown causes, anomalous muscle or anomalous vessel should be kept in mind.