Rotational acetabular osteotomy (RAO) has an important advantage in that surgical bony defects are reconstructed with a patients' own tissue. We propose a surgical robot for the RAO using Er:YAG laser irradiating mounted on iliac bone to operate RAO precisely and to reduce recovery and trauma. A water-cooling Er:YAG laser (30 J/cm/sup 2/, l=2.94 mum, 20 Hz, 200 msec) that used optical fiber was operated 4-8 irradiation-overlapping ratio. We kept the distance between the laser and the bone at 0.25 mm using force sensor and spring to maintain effective ablation. Swine scapulae were ablated and performance was evaluated. The manipulator was operated mounting on iliac bone to get a filed position whereby resulting in precise bone cutting. The precision of the manipulator was within 0.3 mm and the efficiency of laser bone ablations per unit time optimized to 0.21 mm/sup 3//secW at the overlapping ratio of the irradiation area was 0.8, meaning a given ablated area was irradiated five times. The troughs showed m charring at this condition and the temperature of the surface was raised to 41.3 degrees C and it lasted only 5 seconds. We are sure that this research will be applied to orthopedics in the near future.