Background.Total knee replacement is a procedure of choice in the management of severe osteoarthritis. Currently two types of prosthesis are widely used, cruciate retaining and cruciate substituting. Experts have not yet reached agreement regarding which one is better. This study is aimed to compare functional outcome between cruciate retaining and substituting prosthesis. Materials and methods.This study was a randomized single-blinded clinical trial. Patients with severe osteoarthritis were divided into two groups and evaluated before operation. First group underwent cruciate retaining total knee replacement, and the other cruciate substituting total knee replacement. Functional outcome was evaluated in 3 and 6 months after operation, regarding the knee flexion angle and International Knee Documentation Committee score.Results.There were 14 patients. Mean knee flexion angle of cruciate retaining in 3 and 6 months were 105.0 degrees and 113.3 degrees respectively, whereas cruciate substituting were 118.1 degrees and 126.2 degrees. International Knee Documentation Committee score of cruciate retaining in 3 and 6 months were 49.0 and 59.4 respectively, while cruciate substituting were 52.6 and 63.8. There were significant differences in flexion angles between cruciate retaining and cruciate substituting groups at 3 months (p=0.006) and 6 months (p=0.018). No significant difference was demonstrated in International Knee Documentation Committee score between cruciate retaining and cruciate substituting groups at 3 months (p=0.053) and 6 months (p=0.240).Conclusions.Functional outcome regarding the knee flexion angle of cruciate substituting group was 13.1 degrees better in 3 months and 12.9 degrees in 6 months compared to cruciate retaining group. Functional outcome based on International Knee Documentation Committee score score did not show significant differences between two groups whether 3 or 6 months after operation.