PURPOSE: The purpose of this study was to determine the results of internal fixation with locking plate system for the unstable proximal humerus fracture. MATERIALS AND METHODS: Sixteen cases of unstable proximal humerus fracture were treated using locking plate system between September 2004 and June 2005. Average age of the patients was 55.6 years (range, 22 to 78), male was four patients, female was twelve. The clinical outcomes were evaluated by using Neer's evaluation criteria and Constant socring system. We analyzed the radiological results by bony union time and Paavolainen method. All data was analyzed statistically. RESULTS: According to Neer's evaluation ciriteria, eleven cases (69%) showed excellent or satisfactory results and according to Constant scoring system, twelve cases (75%) showed excellent or good result. Twelve cases (75%) showed good results by Paavolainen method. In all cases, bony union was obtained in average 12.8 weeks after operation. There were two complications; one screw irritation and one screw loosing. CONCLUSION: The patients treated using locking proximal humerus plate could exercise earlier due to good initial stability. And the clinical and radiological results were relatively good. The treatment of unstable proximal humerus fracture with locking plate system was considered as a good method.