PMMA/clay nanocomposites are prepared by emulsifier-free emulsion polymerization. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to characerize the distribution of clay in the polymer matrix mid observe the morphology of the resulting nanocomposites respectively. The exfoliated nanocomposites were successfully prepared up to 10 wt% pristine Na+ -MMT incorporation. Compared to neat PMMA, the glass transition temperature and storage modulus of PMMA/clay nanocomposites became higher without significant increase in refractive index. PMMA/clay nonocomposites were found to retain over 70% of transparency, which is important for optical applications.