Supercritical carbon dioxide is known to swell and plasticize poly(methyl methacrylate), PMMA, dramatically. In this paper, a basic characterization of the solid-state foam processing is presented. Experiments were conducted in order to determine the effect of foaming temperature and foaming time on cell structures, cell density, and so on. As a result, higher foaming temperature and foaming time generated larger cell size, and lower cell density.