Neurogenesis in the adult hippocampus is differentially influenced by the genetic background. We examined the differences in Ki-67 (a proliferating cell marker) and doublecortin (DCX; an immature progenitor cell marker) immunolabelling in the dentate gyrus (DG) of the adult hippocampus in three strains of mice (ICR, C57BL/6, and BALB/c) to evaluate the effect of genetic background on adult hippocampal neurogenesis. All strains showed constitutive immunoreactivity of either Ki-67 or DCX in the DG of the adult hippocampus. C57BL/6 mice showed significantly higher levels of Ki-67-immunopositive cells in the subgranular zone (SGZ) of the DG (approximately 2.2-fold) compared to ICR and BALB/c mice. The greatest number of DCX-immunopositive cells was found in C57BL/6 (approximately 1.6-fold), which differed significantly from ICR and BALB/c mice. However, there was no significant difference in the number of Ki-67- and DCX-immunopositive cells between BALB/c and ICR mice. Genetic differences with respect to certain aspects of hippocampal neurogenesis in adult mice may influence hippocampal functions, including learning and memory.