Objective: Evaluate the effects of primary total knee arthroplasty in patients with severe osteoarthritic knees. Material and method: Prospective observation,data are represented by descriptive statistics (SPSS 13.0 soft-ware). From 7/2010 to 6/2011, 21 primary total knee prostheses were implanted in 21 patients. Patients were evaluated with the use of Knee Score (KS) and Knee Function Score (KFC). Results: A total of 21 patients with 21 knee were donefix - bearing posterior - stabilized prosthesis. At an average of 6 months followup for 21 patients. The mean pre-and post-of KS improved from 40.09 + or - 5.08 to 81.12 + or - 17.16 respectively, the mean pre-and post-of KFS improved from 41.08 + or - 6.01 to 80.02 + or - 20.18 respectively (p0.05). The average flexion was 110 + or - 5° .The proportion of post-op KS score was 33.33 percent of excellent, 61.9 percent of good, 4.76 percent of fair, 0 percent of poor. The complication of postoperation was the pain of patellofemoral articulation of one patient. Conclusion: TKA mostly improves knee joint function in the patients with severe osteoarthritic knees. Long term follow up is needed to evaluate farther complications.