This study was undertaken to clarify the relationship between pelvis movement strategy, head-arm-trunk (HAT) movement strategy, and the strength of pelvic surrounding muscles in patients with knee osteoarthritis (OA). The subjects were 14 outpatients with knee OA, 11 of whom were evaluated both limbs and 3 were evaluated unilateral limb. We classified the pelvis movement and HAT movement strategy from a photograph of single leg standing on the frontal plane which inclined an angle of the acromion,trunk and adduction of the hip joint. We compared the maximum isometric contraction of gluteus medius muscle, gluteus maximus muscle and adductor muscle about the difference between the pelvis movement and HAT movement strategy. As the results,we found out two important clinical aspects. First, the muscle strength of gluteus medius muscle of HAT movement strategy was significant decreased. Second, the gluteus medius muscle strength and the inclined angle between the acromion and trunk were negatively correlated with HAT movement strategy. The present study suggests that we may estimate the weakening trend of gluteus medius muscle from the single leg standing when we observe HAT movement strategy in knee OA.