Interpenetrating polymer networks of polyurethane, based on poly(oxypropylene)triol grafted with polyacrylonitrile and epoxy, were prepared by a simultaneous polymerization technique. The mechanical properties and morphology of the networks were investigated. As the epoxy content increased, the tensile strength of the interpenetrating polymer networks or the graft networks (in which some grafting reaction has taken place between polyurethane and the pendant hydroxyl group of epoxy) decreased. The shifts of the loss modulus peaks of the interpenetrating polymer networks and the graft-IPNs were different and their tan delta peaks shifted to a high temperature as the epoxy content increased.