Microglia are resident immune cells of the central nervous system, and play crucial roles in brain development by regulating the number of neural precursor cells. Recent study showed microglia surrounding the subventricular zone express osteopontin (OPN) during brain development. OPN is a phosphoglycoprotein involved in immune responses, cancer metastasis, and cell proliferation. However, it remains unclear whether OPN in microglia is involved in brain development. In this study, we investigate the contribution of OPN secreted from microglia to the proliferation of neural precursor cells. We examined the expression of integrin αvβ3, and CD44, which are receptors for OPN, in neural precursor cells, and found that neural precursor cells express integrin αvβ3, but not CD44. To examine whether microglia promote the proliferation of neural precursor cells by OPN-integrin αvβ3 signaling, we performed co-culture experiment of microglia and neural precursor cells across the transwell in the presence of OPN neutralizing antibody or cilengitide, an inhibitor for integrin αvβ3. Our study indicates signaling between OPN and integrin αvβ3 is a crucial contributor to regulate the proliferation of neural precursor cells mediated by microglia during brain development.