Objective: To investigate changes in hip and knee muscle strength in patients before and after total hip arthroplasty (THA) in comparison with that in healthy adults. Methods: The study included 21 women who underwent unilateral THA (THA group) and 21 age-matched healthy women (healthy group). Maximal isometric strengths of hip fl exors, extensors, and abductors, and knee extensors and fl exors were measured before surgery and at 4 weeks and 6 months after surgery. Results: Before surgery, muscle strength on both sides, except for hip fl exors on the uninvolved side, was signifi cantly lower in the THA group than the corresponding muscle strength in the healthy group. Up to 6 months after THA, strength of all muscle groups on both sides was signifi cantly improved compared with their preoperative status, although the knee extensor strength on the involved side temporarily worsened at 4 weeks. However, the strength of hip extensors and knee extensors on the involved side, and hip abductors on both sides in the THA group remained below that in the healthy group. Conclusions: Our results suggest that rehabilitation specialists should consider increasing the focus on the uninvolved side and encourage patients to continue strength training beyond 6 months after surgery.