CNS microglia have long been considered as resident immune cells, which are activated in response to pathological events. However, increasing evidence suggests that they also have physiological roles in the development of the normal central nervous system (CNS). In this study, we found large numbers of activated microglia in the forebrain subventricular zone (SVZ) of the rat from P1 to P10. Pharmacological suppression of the activation by minocycline, which produces a decrease in levels of a number of proinflammatory cytokines, i.e., IL-1β, IL-6, TNF-α, and IFNγ, significantly inhibited neurogenesis and oligodendrogenesis in the SVZ. In vitro neurosphere assays reproduced the enhancement of neurogenesis and oligodendrogenesis by activated microglia. Interestingly, any single function-blocking antibody to IL-1β, IL-6, TNF-α, or IFN-γ, did not change the effects of activated microglia on neurogenesis and oligodendrogenesis, however, the effects were significantly suppressed by a mixture of all of these function-blocking antibodies. These results suggest that activated microglia accumulate in the early postnatal SVZ and that they enhance neurogenesis and oligodendrogenesis via complementary effects of released cytokines.