The Primary objectives of total hip replacement arthroplasty are not only to relieve pain, but to improve motion and function. The range of motion following total hip replacement arthroplasty depends on several factors, especially the position of acetabular cup and femoral stem. Also the oriental need more flexion and abduction in hip motion for squarting position as compared with the European who have different living activity. We studied in vitro biomechanical evaluation of proper position of acetabular cup and femoral stem for T.H.R.A. The following results were obtained: l. Effect of component orientation on R.O.M. 2. Acceptable position of prosthesis was as follows: Acetabular cup: inclination 40–50 degree, anteversion 20–30 degree, Femoral stem: anteversion 0–10 degree. 3. The sum of ideal anteversion of the two components was 30–35 degree 4. Oriental sitting position was performed normally in the ideal position of the prosthesis 5. Acetabular cup is likely insert in the position as far as post sup rim of acetabulum mightbe feasible to be full recovered.