Highly transparent poly(methyl methacrylate) (PMMA) composites have been made by carefully matching the refractive index of the glass fiber reinforcement with the PMMA matrix. Composites containing 10.4 vol% glass fibers and 0.68 mm in thickness had an overall optical transmission of 92%. The transparency of the composites is temperature dependent because of the different temperature coefficients of refractive index for the glass fiber and PMMA. The tensile strength of the composites at room temperature was twice that of pure PMMA and decreased with increasing temperature, as predicted by the rule of mixtures.