In the early 1970s, Bateman and Giliberty in North America and Monk in Europe introduced the bipolar endoprosthesis. This design allowed the movement between the acetabulum and the outer metal shell as well as between the high-density polyethylene socket and the ball of the femoral components. But the motion of two components in bipolar endoprosthesis has been argued in another several reports, depending on the type of cup and the condition of the hip until now. The authors reviewed 20 hips of the Universal Hip Replacement bipolar endoprosthesis without acetabular reaming(A group) and 23 hips of the Universal Hip Replacemet bipolar endoprosthesis with acetabular reaming(B group). The motion and its amount of the two components are also analyzed in radiologic study. The follow up period of the hip ranged from 1.5 months to 22.1 months, and the average length was 12 months. The following results were obtained. l. In A group, there were both of the outer and inner bearing motion in 18 cases(90.0%), and the outer bearing motion in 2 cases(10.0%). In B group, there were both of the outer and inner bearing motion in 13 cases(56.5%), and the inner bearing motion in 10 cases(43.5%). The ratio of both bearing motion in A group was more than those in B group (p<0.05). 2. In A group, the total average amount of the motion was 42°, the average amount of the outer bearing motion and the inner bearing motion were 30°(71.4%) and 12°(28.6%), respectively. The amount of the outer bearing motion was larger than that of the iner bearing motion in A group(p<0.05). In B group, the total average amount of the motion was 37°, the average amount of the outer bearing motion and the inner bearing motion were 10°(27.0%) and 27°(73.0%), respectively. The amount of the inner bearing motion was larger than that of the outer bearing motion in B group(p<0.05). The total average amount of the motion in A group was slightly larger than that in B group, but there was no difference statistically(p>0.05).