Diabetic retinopathy (DR) is a microvascular complication of diabetes mellitus (DM) and is the leading cause of blindness worldwide. Numerous studies have shown that supplementing with amino acids such as hydroxyproline, lysine, and glycine can provide protective benefits against proliferative diabetic retinopathy. This study aimed to evaluate the potential preventive effect of glycine against diabetic retinopathy in STZ-diabetic rats. Method: Eighty-four female Wistar rats, aged 8 to 12 weeks, were used in the study. The rats were divided into four groups: a control group, a glycine group (G), a diabetic retinopathy group (DR), and a diabetic retinopathy group administered glycine (DR+G). Electroretinographic (ERG) and histopathological studies were conducted to assess the protective role of glycine on the retinas of the rats. Results: The electroretinographic and histological findings for the glycine group showed no significant differences from the control retina. In contrast, severe changes were observed in the DR group, leading to a decrease in ERG parameters and alterations in retinal structure, particularly after four weeks. For the DR+G group, the electroretinographic data indicated no differences from the control retina at both the two-week and four-week marks. The histological cross-sections taken after four weeks showed an intact retina and vitreoretinal interface. Conclusion: This study provides evidence that the administration of glycine can repair both the structure and function of the retina. Additionally, supplementing the diet of experimental DR rats with glycine demonstrated a protective effect against the retinal damage typically associated with diabetic retinopathy.