OBJECTIVE: To verify the effect of low energy laser irradiation (LELI) on the regeneration of injured sciatic nerve of the rat by showing the functional improvement and the elevated immunoreactivities (IRs) of growth-associated protein 43 (GAP-43). METHOD: Twenty rats, which had standardized compression injuries to the sciatic nerves, received the calculated LELI therapy immediately after the nerve injury and four consecutive days. The functional status was evaluated by sciatic functional index (SFI), and GAP-43-IRs was evaluated by immunohistochemistry and RT-PCR. RESULTS: The SFI was recovered in LELI rats faster than in the control group. Although expression of GAP-43 in the injured sciatic nerve was increased both in the LELI and control groups, the intensities of GAP-43-IRs were much greater in LELI treated group at 1 and 3 weeks after nerve injury. Both SFI and GAP-43-IRs reached the same level at 5 weeks after the nerve injury. CONCLUSION: LELI enhanced the neural regeneration after experimentally induced sciatic nerve injury at the early stage of recovery. Considering the effect of LELI on nerve regeneration was not fully explained until now, this study could suggest the meaningful explanation on the mechanism of LELI effectiveness on neural regeneration.