A series of castor oil polyurethane/poly(methyl methacrylate) interpenetrating polymer networks (IPNs) and gradient IPNs, cured at room temperature, were prepared by a simultaneous IPN method. The polymerization processes were traced through IR techniques; results for the morphology and miscibility among multiple phases of materials, obtained by transmission electron microscopy, indicated that the systems belonged to graft-mode IPNs, and the domains between two phases were controlled on a nanometer scale, Thermomechanical analysis detection results showed that through interpenetration between networks, the glass-transition temperatures of the systems could be linked up effectively. Furthermore, the systems were combined with selected barium titanate superfine fibers. The composite techniques were determined, and the thermoelectric and mechanical properties were examined in detail.