A 45 year-old man underwent Chiari pelvic osteotomy and valgus femoral osteotomy. Twenty weeks after surgery, muscle strength and range of motion were recovered; however, the patient exhibited Trendelenburg gait. We examined changes in electromyogram activity around the hip joint. The mean muscle activity initiation time was -0.27 sec. in the tensor fasciae latae, +0.15 sec. in the gluteus medius, +0.12 sec. in the gluteus maximus upper fiber, and +0.12 sec. in the gluteus maximus lower fiber (“+” means before initial heel contact;“-” means after initial heel contact). These were delayed compared with normal timing, especially in the tensor fasciae latae muscle. Delayed muscle activity initiation time of tensor fascia latae can cause Trendelenburg gait.