For in vitro myelination system, Schwann cells and neuronal cells of rat were cocultured. Schwann cells and neuronal cells, respectively, were obtained from dorsal root ganglion of rat embryos (E15). This method includes four steps: first step of suspension of the embryonic dorsal root ganglion cells, second step of addition of anti-mitotic cocktail, third step of purification of dorsal root cells, and fourth step of addition of Schwann cells to dorsal root ganglion cells. We made a highly purified population of myelination in a short period through this procedure and identified myelination basic protein using antibody of myelination basic protein.