In the present study, we investigated the time-course changes of neuronal degeneration and microglial activation in the gerbil dentate gyrus after transient cerebral ischemia using Fluoro-Jade B histofluorescence staining and immunohistochemistry for Iba-1. Fluoro-Jade B positive cells were observed from 6 hr and markedly increased 1 day after ischemia/reperfusion. Iba-1-immunoreactive microglia were increased and hypertrophied at early time, and Iba-1 immunoreactivity was highest at 2 days after ischemia/reperfusion. These results may be direct evidence on neuronal degeneration and microglial activation in the gerbil dentate gyrus after ischemia/reperfusion.