Platelet-derived growth factor receptor alpha (PDGFR alpha) is a marker of oligodendrocyte precursor cells in the central nervous system. NG2 is also considered a marker of oligodendrocyte precursor cells. However, whether there are differences in the distribution and morphology of oligodendrocyte precursor cells labeled by NG2 or PDGFR alpha in the developing neonatal rat brain remains unclear. In this study, by immunohistochemical staining, NG2 positive (NG2(+)) cells were ubiquitous in the molecular layer, external pyramidal layer, internal pyramidal layer, and polymorphic layer of the cerebral cortex, and corpus callosum, external capsule, piriform cortex, and medial septal nucleus. NG2(+) cells were stellate or fusiform in shape with long processes that were progressively decreased and shortened over the course of brain development. The distribution and morphology of PDGFR alpha positive (PDGFR alpha(+)) cells were coincident with NG2(+) cells. The co-localization of NG2 and PDGFR alpha in the cell bodies and processes of some cells was confirmed by double immunofluorescence labeling. Moreover, cells double-labeled for NG2 and PDGFR alpha were predominantly in the early postnatal stage of development. The numbers of NG2(+)/PDGFR alpha(+) cells and PDGFR alpha(+) cells decreased, but the number of NG2(+) cells increased from postnatal days 3 to 14 in the developing brain. In addition, amoeboid microglial cells of the corpus callosum, newborn brain macrophages in the normal developing brain, did not express NG2 or PDGFR alpha, but NG2 expression was detected in amoeboid microglia after hypoxia. The present results suggest that NG2 and PDGFRa are specific markers of oligodendrocyte precursor cells at different stages during early development. Additionally, the NG2 protein is involved in inflammatory and pathological processes of amoeboid microglial cells.