Recent evidence suggests that adult neurogenesis contributes to the pathophysiology of different psychiatric disorders, including depressive disorder, anxiety disorder, and schizophrenia. Seasonal affective disorder (SAD) is a specific form of recurrent depressive disorder that can be induced by shortened light period. It is unclear yet whether neurogenesis is affected in SAD or under altered light/dark cycle. The present study aims at examining whether neurogenesis and dendritic growth of immature neurons are affected in Mongolian gerbils, a mainly diurnal rodent, under light deprivation. Animals were divided into two groups: the control (kept in 12 h light:12 h dark) and the light-deprived groups (kept in 24 h dark). Depression-like behaviors and neurogenesis were assessed after 2 weeks. Compared with the control group, light-deprived gerbils showed increased immobile time in the tail suspension test and forced swimming test, which indicates induction of depression-like behavior. Cell proliferation in both the hippocampal and subventricular zone were significantly decreased in the light-deprived group, which also showed a decreased neuronal differentiation. Dendritic maturation of immature neurons was suppressed by light deprivation, which is revealed by doublecortin staining and Sholl analysis. The results revealed that the light/dark cycle exerts impacts on neurogenesis and maturation of new neurons. Additionally, the current experiment may offer a model for exploring the relationship among daylight exposure, circadian cycles, depressive behavior, and the underlying mechanisms.