In this study, we investigated whether sildenafil, a cyclic guanosine monophosphate-dependent phospodiesterase-5 inhibitor, could promote functional nerve regeneration after surgical section and repair of the sciatic nerve in rats. Nerve regeneration was studied in a rat sciatic nerve transected and repair model. The animals were randomly assigned to one of the following 3 treatment groups (n = 20/group): sildenafil-treated group 1 (5 mg/kg/d subcutaneously, for 7 days), sildenafil-treated group 2 (5 mg/kg/d subcutaneously, for 42 days), and control group given saline solution (once per day subcutaneously). Walking track analysis, electromyography, and histological evaluation were performed on day 90 after repair operation. The results showed that the sciatic functional index of sildenafil-treated group 1 (data) was slightly better than that of sildenafil-treated group 2 (data) and control group (data) on postoperative day 90. However, the difference was not statistically significant (P = 0.073). No significant differences of the motor nerve conduction velocity were found between experimental groups [18 (2.4) and 20 (4.1 m/s)] and saline control group [19.5 (3.0) m/s] (P = 0.68). Comparison of myelinated axon count of regenerated nerve of the rat between the sildenafil-treated group 1, sildenafil-treated group 2, and saline group was also not significantly different (P = 0.56). In conclusion, administration of sildenafil after nerve repair surgery was found to have positive but insignificant effects on several parameters of nerve regeneration. Further studies could clarify this trend suggesting enhanced nerve regeneration mediated by sildenafil.