This paper describes the preparation, characterization, and the permeation properties of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) dense polymer films containing fullerenes (C-60). The C-60 are either dispersed or covalently bonded to PPO at various concentrations. The gas permeability results are very different between covalently bonded and dispersed PPO-C-60. The gas permeability of PPO-C-60 bonded increases up to 80% with increasing fullerene concentration. The gas pair selectivity, however, stays constant. This behavior is probably due to stiffening of the polymer structure and increase of free volume. The gas permeability through the PPO-C-60 dispersed decreases in comparison to pure PPO. This reduction is due to C-60 clustering in the polymer. The clusters seem to induce polymer crystallinity, and they are probably aligned along the film plane, creating an extra barrier for gas permeation.