We recently showed that suppressing cell cycle progression inhibited reactive astrogliosis and promoted neuronal survival in an acute focal cerebral ischemia rat model. However, it remains unclear whether and to what extent the beneficial effects of cell cycle inhibition might also be attributed to the inhibition of microglial proliferation and cytokine/chemokine production. In this study, we showed that application of the cell cycle inhibitor roscovitine before middle carotid artery occlusion (MCAO) in the rat inhibited microglial proliferation and cytokine/chemokine production, and reduced the number of cell-cycle-related proteins including cyclin A, cyclin B, and cyclin E. All of these microglia-related changes may contribute to roscovitine's effect on reducing neuronal apoptosis and infarct volume, thus improving neurological scores. Using the BV-2 microglia cell line, we showed that roscovitine not only inhibited oxygen-glucose deprivation (OGD) induced cell cycle activation by arresting the cells at G1/S and G2/M in a dose-dependent manner, but it also inhibited interleukin-1 beta (IL-1β), macrophage inflammatory protein-1α (MIP-1α), and nitric oxide (NO) production. These results suggest that cell cycle modulation results in neuroprotection in ischemia, mediated at least in part through inhibition of microglia proliferation and production of inflammatory cytokines such as IL-1β, MIP-1α, and NO. © 2008 Wiley-Liss, Inc.