Magnetization, electrical conduction, and magnetoresistance (MR) of C(60)-Co nanocomposites, where Co nanoparticles are dispersed in C(60) molecules, have been investigated over a wide temperature range and Co volume fraction. The C(60)-Co nanocomposites exhibit MR when the Co volume fraction is controlled in such a way that the conduction mechanism is dominated by tunneling of carriers between Co nanoparticles in the C(60) matrix. The MR, which is attributed to spin-polarized tunneling through the C(60) molecules, shows strong temperature dependence. Our results indicate that some paramagnetic components contribute to the observed MR. The material-dependent bias-voltage dependence of the MR ratio suggests that these paramagnetic components originate from the interface between organics and ferromagnets. The present study advances the fundamental understanding of spin-dependent transport in organic semiconductors.