ObjectiveTo evaluate the photoreceptor-protective effects of Cdk5 inhibitor Roscovitine on retinal degeneration in Royal College of Surgeons (RCS) rat. MethodsThe RCS rats were divided into three groups according to postnatal days: the early (17 days), medium (25 days) and late intervention group (35 days). Cdk5 inhibitor Roscovitine were used in the right eyes by intravitreal injection as experimental eyes and Roscovitine solvent dimethylsulfoxide were used in the left as control at postnatal 17, 25, 35 days. Hematoxylin-eosin (HE) staining was used to observe the thickness of outer nuclear layer. The expression of Cdk5 P25 and cleave-caspase 3 in the retina was evaluated by immunohistochemistry. The protein expression of cleave-caspase 3 in the retina was determined by Western blot. The apoptosis of retinal cells was examined by terminal-deoxynucleotidyl transferase mediated nick end labeling. ResultsHE staining showed that thickness of outer nuclear layer in the early and medium intervention groups were significantly thicker than that in the control group (P < 0.05), particularly in the early intervention group. And there was no significant change in the late intervention group (P > 0.05). The expression level of Cdk5, p25, cleave-caspase 3 in the outer nuclear layer in three intervention groups were lower than that in the control group (P < 0.05), especially in the early intervention group. ConclusionCdk5 inhibitor Roscovitine can delay the retinitis pigmentosa process in RCS rats by early, medium interventional therapy and may have a certain degree of photoreceptor-protective effects.