Purpose: The Protective Effect of Dimethylthiourea (DMTU) against photic injury of the retina was evaluated by electroretinogram (ERG).Methods: In the DMTU-treated group, 250, 500, or 750 mg/kg DMTU was administered intraperitoneally to albino rabbits at 24 hours and immediately before starting light exposure to the eye. In the control group, physiological saline was injected intraperitoneally instead of DMTU. Preservation rates of ERG a-, b- and c-wave amplitudes were defined as the percentages of the post-photic injury values to the pre-photic injury ones, and were compared between the control and the DMTU-treated groups.Results: In 750 mg/kg DMTU-treated group, the preservation rate of the a-wave was significantly higher than that in the control group 24 hours after the photic injury. While the preservation rate of the c-wave was remarkably low in the control group 24 hours after the photic injury, it was significantly higher in the 500 and 750 mg/kg DMTU-treated groups. Furthermore, better preservation rates of the c-wave were noted with higher doses of DMTU.Conclusion: These results suggest that DMTU protects against photic injury of the retinal pigment epithelium and photoreceptors.