Novel biocomposites have been prepared by the free radical polymerization of a lung oil-based resin using spent germ, the coproduct of wet mill ethanol production, as a filler. The effect of filler particle size, amount of filler, amount of crosslinker, and molding pressure on the resulting composites has been investigated. When compared to the pure resin, an increase in storage modulus is observed when filler is added to the matrix. The thermal stabilities of the resulting composites lie between the stabilities of the resin and the spent germ. Decreasing the particle size results in an increase in both the storage modulus and the mechanical properties of the composites. As the amount of crosslinker, divinylbenzene, increases, an improvement in the thermal stabilities and mechanical properties is observed. The composites prepared are mainly composed of renewable resources, possess good thermal and mechanical properties, and have potential applications in the construction and automotive industries. (c) 2008 Wiley Periodicals, Inc.