Antioxidant-like protein-1 (AOP-1) reduces the intracellular level of reactive oxygen species. In the present study, the age-related change in AOP-1 expression in the hippocampus among young, adult and aged gerbils was compared using western blot analysis and immunohistochemistry. The results demonstrated that the protein expression of AOP-1 was gradually and significantly increased in the hippocampus during the normal aging process. In addition, the age-dependent increase in AOP-1 immunoreactivity was also observed in pyramidal neurons of the hippocampus proper; however, in the dentate gyrus, AOP-1 immunoreactivity was not altered during the normal aging process. These results indicated that the expression of AOP-1 is significantly increased in the hippocampus proper, but not in the dentate gyrus, during the normal aging process.