Aims: To investigate the effects of ultraviolet radiation (UVR) on cataract development in rat lenses and whether or not N-acetyl serotonin has an effect on changes in these lenses. Material and Methods: The study was performed using 5 groups of Sprague-Dawley albino rats, with each group consisting of 15 rats. The 5th group being the control group did not receive any applications, whilst the other 4 groups received a daily dose of 0.2 J/ cm(2)/day UVR (305 nm wavelength) for 60 days. A dose of 4 mg/kg/0.1 ml N-acetyl serotonin was injected intraperitoneally to group 1 and group 2 every day and on alternate days, respectively. Group 3 received an intraperitoneal injection of 0.1 ml phosphate buffer solution every day, whilst group 4 received no injection. On the 60th day, an intracardiac withdrawal of blood was performed, after the rats had been anesthetized with ether. Following the withdrawal of blood, the rats were killed using a high dose of ether and their eyes were enucleated. The lens fresh weights, plasma malondialdehyde (P-MIDA), erythrocyte glutathione peroxidase (E-GSHPx), erythro(B-RGSH), erythrocyte catalase (E-CAT), lenticular malondialdehyde, lenticular superoxide dismutase (L-SOD), lenticular glutathione peroxidase (L-GSHPx) and lenticular glutathione (L-GSH) levels were all assessed. Results: The lens fresh weights were determined to be lower in group 1 and in the control group in comparison with the other groups (p < 0.01). Whilst the P-MDA level was found to be lower (p < 0.001), the E-GSHPx level was higher (p < 0.01) in the control group than in the other groups. The E-GSHPx level was higher in groups 1 and 2 than in groups 3 and 4 (p < 0.01). The B-RGSH level was higher in the control group than in the other groups (p < 0.001). The E-CAT level was higher in both the control group and group 1 than in groups 2, 3 and 4 (p < 0.01), whilst it was higher in group 2 when compared to groups 3 and 4 (p < 0.01). The L-SOD levels were found to be higher in the control group and group 1 than in groups 2, 3 and 4 (p < 0.001). Whilst the L-GSHPx levels were determined to be higher only in the control group (p < 0.001), the L-GSH levels were higher in the control group and group 1 than in the other groups (p < 0.001). Conclusions: In recent years, the depletion of the atmospheric ozone layer has resulted in the penetration of more UVR to the earth, which causes various effects on different tissues of organisms. N-acetyl serotonin, a melatonin precursor, may well be effective in the prevention of the negative effects induced by the UVR upon the lens tissue, in which case the capability of melatonin to capture free radicals as well as its antioxidative properties should be taken into consideration.