Aims: Melatonin modulates the function of nervous system and its secretion is dependent to circadian rhythms and visual signals. The melatonin receptors are founded in many areas of the brain. During critical period of the brain development, the structure of mammals’ brain is intensely affected by peripheral sensory signals. The aim of this study was to evaluate the effect of interaction of age and visual deprivation during critical period of brain development on melatonin receptors expression in rats’ hippocampus. Materials & Methods: This experimental study was carried on 2 groups (n=36) of male Wistar rats kept in standard 12 hour light/dark condition (Light Reared-LR) or in complete darkness (Dark Reared-DR). The rats of each groups, were introduced into the experiments at 2, 4 and 6 weeks old of age. Expression of mRNA of both melatonin receptors, MT1 and MT2, in the hippocampus was evaluated by RT-PCR and using Western Blot technique, protein expression of those receptors was investigated. Data were analyzed by one-way ANOVA with Tukey post hoc tests. Findings: The relative expression of mRNA and protein of MT1 and MT2 receptors increased about 36% in the LR animals from 2 to 6 weeks old of age (p<0.001). The visual deprivation caused a decrease of 35% and 50% in expression of MT1 and MT2 from 2 to 6 weeks old of age, respectively (p<0.001 for both comparison). Conclusion: The relative expression of both melatonin receptors in rats’ hippocampus increases across aging during critical period of brain development and visual deprivation reverses the pattern of melatonin receptors expression.