PURPOSE: To evaluate the effect of decreasing tibial slope on extension gap during posterior stabilized total knee arthroplasty. MATERIALS AND METHODS: One hundred and ten cases of total knee arthroplasty which were done with posterior stabilized implant were included and we divided those into Group I; having flexion contracture (n=35) and Group II; no flexion contracture (n=75), and from each group, we evaluated the relationship between degree of decreased angle of tibial slope and frequency of additional resection of distal femur which was done for compensating insufficient extension gap during total knee arthroplasty and compared frequencies of additional distal femoral resections between 2 parts having more and less degree of decreased angle of tibial slope. RESULTS: In Group I and II, tibial slope decrease were 8.7degrees, 7.4degrees (p=0.145) and frequencies of additional resection were 51.4%, 24% (p=0.005) in average. Comparing 2 parts having more and less degree of decreased angle of tibial slope in each Group, frequencies of additional resection were 44.4%, 58.8% (p=0.505) and 13.2%, 35.1% (p=0.032). CONCLUSION: During posterior stabilized total knee arthroplasty, especially having no preoperative flexion contracture, decreasing tibial slope can be considered as a factor influencing on extension gap by removing greater anterior bone and the estimation of predictable tibial slope decrease through preoperative radiologic findings can be helpful in creating equal flexion and extension gaps.