The effect of a structure of a fullerene derivative on electronic properties of poly(3-hexylthiophene)/fullerene composite was studied at 3 cm wave band EPR in wide (77-320 K) temperature region. All the systems with different fullerene derivatives demonstrate sum spectrum of small polarons with different mobilities and contributions depending on the structure of the fullerene derivative. Both the spin-lattice and spin-spin relaxation times were determined separately by using the steady-state saturation method. The treatment of polymer matrix by fullerene derivative changes its dimensionality and conformation. This leads to the change in the spin relaxation and susceptibility as well as in the rate of polaron diffusion along polymer chain.