The porosity of suspension copolymers of methacrylic acid (MA) and divinylbenzene (DVB) has been studied. The copolymers were prepared both directly from monomer blends and with toluene or n-octane as inert diluents. The pore volume and radii of pores were larger for copolymers containing 5.0% of DVB than those for copolymers containing 9.1% of DVB. The volume and radii of pores increased with increasing diluent content, but the effect of n-octane was more pronounced than that of toluene. Based on considerations of monomer reactivities and copolymer-diluent and copolymer-unreacted monomer interactions, the following model of structure of MA and DVB copolymers has been proposed: The copolymers are composed of microgels interconnected into a rigid skeletonlike structure, surrounded by lightly crosslinked and unentangled poly(methacrylic acid) chains.