A comparative study of the hydrodynamic and electrooptical properties of solutions of donor-acceptor complexes formed between C₆₀ and poly(2,6-dimethyl-1,4-phenylene oxide) and poly(N-vinylpyrrolidone) with those of individual polymers showed that even an insignificant amount of C₆₀ (from 0.5% to several percent) incorporated into the complex shows a strong effect on the molecular parameters of polymers. It was demonstrated that for complexes containing no more than one polymer molecule per fullerene molecule, the effective hydrodynamic sizes in solution are increased, whereas their shape asymmetry is reduced compared to the molecules of the original polymers.