Neural stem cells (NSCs) have the features of both neural progenitors and stem cells, and show great potentials in translational research and regenerative medicine. Studies on NSCs have been greatly accelerated by the introduction of induced neural stem cells (iNSCs). The iNSCs are usually differentiated from induced pluripotent stem cells (iPSCs) or transdifferentiated from somatic cells such as fibroblasts or glial cells. Here, we describe a detailed protocol to reprogram human and mouse fibroblasts into iNSCs by overexpression of a transcription factor Ptf1a delivered by lentiviruses. The obtained iNSC lines have a strong self-renewal ability and are capable of differentiating into various types of neurons, astrocytes, and oligodendrocytes both in vitro and in vivo. The protocol is quite simple but powerful to produce iNSC lines.