Endogenous tri-potential neural stem cells (eNSCs) exist in the adult spinal cord and differentiate primarily into oligodendrocytes (OLs) and astrocytes. Previous in vivo and in vitro studies have shown that during development proliferation and differentiation of oligodendrocyte progenitor cells (OPCs) depend on activity in neighboring axons. However, this activity-dependent development of OPCs has not been examined in the adult CNS. In the present study, we stimulated unilateral corticospinal (CS) axons of the adult rat and investigated proliferation and differentiation of OPCs in dorsal corticospinal tract (dCST). eNSCs were labeled with the mitotic indicator 5-bromo-2′-deoxyuridine (BrdU). Phenotypes of proliferating cells were identified by double-immunolabeling of BrdU with a panel of antibodies to cell markers: NG2, Nkx2.2, APC, GFAP, and Glut-1. Electrical stimulation of CS axons increased BrdU labeled eNSCs and promoted the proliferation and differentiation of OPCs, but not astrocytes and endothelial cells. Our findings demonstrate the importance of neural activity in regulating OPC proliferation/differentiation in the mature CNS. Selective pathway electrical stimulation could be used to promote remyelination and recovery of function in CNS injury and disease.