In this paper, we evaluated the postural balance of patients with pelvic asymmetry in sitting. 6 subjects which were diagnosed pelvic asymmetry with leg length discrepancy on left and right side participated in this study. We assessed the angle variation using measurement system based on accelerometer and muscle activity of external oblique, thoracic erector spinae, lumbar erector spinae, and lumbar multifidus in the anterior-posterior and left-right direction. The results show that patients with pelvic asymmetry has asymmetric sitting posture with imbalance in trunk muscles. Results from this study can be used to provide useful information about patients with pelvic asymmetry in rehabilitation medicine.