This study was performed to evaluate the effects of low-intensity ultrasound application to the peripheral nerve injury animal model on enhancement of nerve regeneration and functional recovery. Using aseptic microsurgical techniques, the sciatic nerve of adult male Sprague-Dawley rats was crushed at the outside of right mid-thigh for 30 seconds with fine forceps. Beginning just after surgery, various continuous-wave ultrasound treatments with intensities of 0.2 W/$cm^2$, 0.5 W /$cm^2$ and 1.0 W /$cm^2$ operated at 1 MHz or sham treatment were applied to the opposite inside of the crush site for 1 minute every other day with a transducer moving speed of 2cm/sec. For evaluation of the progress of sciatic nerve regeneration, c-Fos expression in the lumbar spinal cord (L4-5) dorsal horn was investigated. c-fos expression was markedly increased at 1hour after sciatic nerve crush injury, then gradually decreased thereafter. The c-fos expressions were significantly decreased (p<0.05) in all the experimental groups in comparison with the control group until 3days post-crush, and the degrees of decrease were higher in 0.5 W/$cm^2$ and 1 W/$cm^2$ intensity ultrasound application groups. It is suggested that low-intensity ultrasound application to an animal model of sciatic crush injury may suppress pain transmission and promote nerve regeneration, and which may result in delayed progress of muscle atrophy and accelerated progress of muscle recovery and eventually may result in accelerated and improved foot function recovery.