Purpose: The purpose of this study is to compare the two prosthesis that used for total ankle arthroplasty. Materials and Methods: From Sept. 2003 to Jun 2006, 13 patients and 14 ankles that could be follow up more than 1 months. Semiconstrained type (Group I, 7 cases) and Unconstrained type (Group II, 7 cases) were used for total ankle arthroplasty. Mean age was 63.2 year-old, 12 ankles are men and 2 ankles were women. Mean follow up periods were 29 months. The criteria to compare the clinical result were postoperative range of motion, AOFAS score and residual bone stock of medial malleolus. Results: Postoperative range of motion of group I was $43.6{pm}9.4$ degrees and of group II was $50.7{pm}7.3$ degrees (p=0.115). Postoperative AOFAS score of group I was $77.1{pm}13.0$ points and of group II was $86.0{pm}5.7$ points (p=0.094). Resected bone stock in medial malleolus of group I was $10.7{pm}2.5;mm$ and of group II was $5.1{pm}1.2;mm$ (p=0.003). Total number of complication in our study was 9 cases. 3 cases were a malleolar fracture, two occurred at intra-operation, the other at follow-up period. Re-operation was done in 6 cases, 3 cases were calcaneal corrective osteotomy, 2 cases were resection of a heterotopic bone and one case was pedicular flap operation for skin problem. Conclusion: In our hospital, mobile bearing type prosthesis shows good result than a semiconstrained type in respect of residual bone stock in medial malleolus. Postoperative range of motion and AOFAS score between two groups shows no significant difference. But small number of patients and short term follow up period is a defect in our study, afterward more population and long term follow up period are needed.