Hippocampal interneurons are local circuit neurons which are responsible for inhibitory activity in the hippocampus. Parvalbumin (PV) is one of useful markers for GABAergic interneurons, not for principle cells, in the hippocampus. In the present study, we investigated age-related changes in PV immunoreactive neurons and protein levels in the gerbil hippocampus during normal aging. PV immunoreactive neurons were detected in all hippocampal subregions of all groups. PV immunoreactive neurons, which innervated principal neurons, were non-pyramidal neurons in the hippocampal CA1-3 regions, and were polymorphic neurons in the dentate gyrus. In the hippocampal CA1 region, the number of PV immunoreactive neurons was significantly reduced in the postnatal month 3 (PM 3) group, which was sustained by PM 18, and, at PM 24, the number of PV immunoreactive neurons was significantly decreased. In the CA2/3 region and dentate gyrus, the number of PV immunoreactive neurons was significantly decreased at PM 6: Thereafter, the number of PV immunoreactive neurons was sustained until PM 24. In addition, changes in PV protein levels in the gerbil hippocampus were similar to immunohistochemical changes during normal aging: PV protein levels were significantly decreased with age by PM 6: Thereafter, PV protein levels were sustained by PM 24. These results suggest that PV immunoreactive interneurons were decreased in the hippocampus with age in gerbils.