Neurons, astrocytes, microglia, and endothelial cells are capable of synthesizing most, if not all, of the complement proteins. Little is known, however, about the capacity of oligodendroglial cells to generate complement components. This study evaluated expression of complement mRNAs and their protein products by human oligodendrocytes. Cells were isolated and cultured from white matter of seven adult cases that had undergone surgical temporal lobe resection for epilepsy. Oligodendroglial cultures were characterized by the expression of such cell type‐specific mRNAs as myelin proteolipid protein (PLP), oligodendrocyte‐specific protein (OSP), and 2′,3′‐cyclic nucleotide 3′‐phosphodiesterase (CNPase) and were further characterized by immunostaining for such differentiation markers as myelin basic protein (MBP), PLP, CNPase, and O4. RT‐PCR analysis showed that the oligodendroglial cells expressed detectable levels of complement mRNAs for the C1q B‐chain, C1r, C1s, C2, C3, C4, C5, C6, C7, C8 γ subunit, and C9. Immunostaining was positive for C1q, C1s, C2, C3, C4, C5, C6, C7, C8, and C9. Double immunostaining for the oligodendrocyte marker O4 and the complement protein C3 demonstrated that all O4‐positive cells were also positive for C3, indicating constitutive C3 expression. These results indicate that oligodendroglial cells may be a source of complement proteins in human brain and thus could contribute to the pathogenesis of several neurodegenerative and inflammatory diseases of the CNS, such as Alzheimer's disease, multiple sclerosis, and progressive supranuclear palsy, where complement‐activated oligodendrocytes are abundant. GLIA 42:417–423, 2003. © 2003 Wiley‐Liss, Inc.