Silicon secondary crosslinked interpenetrating polymer networks (IPNs) of poly(methyl acrylate-co-acrylic acid) (PMAA) and SiO2 were prepared and characterized. The effects of composition, water content, and substrate plate on the phase morphology of the IPNs of PMAA/SiO2 have been studied by scanning electron microscopy, and the glass transition temperature measured by differential scanning calorimetry. By controlling the synthetic conditions an optically transparent film was obtained, which shows a remarkably high degree of mixing between the two chemically dissimilar phases.