We investigated the age-related alterations of astorocyte, oligodendrocyte and microglia in the mouse hippocampal CA1 sector under the same conditions using immunohistochemistry. Glial fibrillary acidic protein (GFAP), 2', 3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) and isolectin B(4) immunoreactivity was measured in 2-, 8-, 18-, 40-42- and 50-59-week-old mice. Total number of GFAP-positive cells was unchanged in the hippocampal CA1 sector up to 40-42 weeks of birth. In 50-59-week-old mice, however, a significant increase in the number of GFAP-positive cells was observed in the hippocampal CA1 sector, exhibiting the morphology of reactive astrocytes. In contrast, the fibers of CNPase immunoreactivity were unchanged in the hippocampal CA1 sector up to 18 weeks of birth. In 40-42- and 50-59-week-old mice, however, a significant decrease in the densities of CNPase-positive fibers was observed in the hippocampal CA1 sector. On the other hand, total number of isolectin B(4)-positive cells was unchanged in the hippocampal CA1 sector up to 40-42 weeks of birth. In 50-59-week-old mice, however, a significant decrease in the number of isolectin B(4)-positive cells was observed in the hippocampal CA1 sector. Our results show that astrocytes proliferate and are activated in the hippocampal CA1 sector with advancing age. Furthermore, the present study demonstrates that the fibers of oligodendrocytes and total number of microglial cells in the hippocampal CA1 sector are decreased during ageing processes. These results suggest that age-related changes of astorocytes, oligodendrocytes and microglia had occurred in the mouse hippocampal CA1 sector.