Organoclay/methyl methacrylate (MMA) nanocomposites were obtained by photopolymerization of the monomers in the presence of organomodified clays using thioxanthone (TX) and ethyl 4-(dimethylamino) benzoate (EDB) as photoinitiating system. The SWy-1 montmorillonite organoclays, SWy-1-C8 and SWy-1-C16, were prepared by ion exchange with octyltrimethylammonium bromide (C8) and hexadecyltrimethylammonium bromide (C16). The photopolymerization rates (R_p) for MMA with different organoclay loadings (0.25; 0.50 and 1.0 wt %) were determined by photodilatometry. The effect on the photopolymerization rate of organoclay concentration, organoclay species and solvent used for dispersion of organoclay were studied. The conversion of monomers with the nanocomposites increased up to 2.5 times with 1.0 wt% of organoclay loading. This behaviour could be attributed to the larger amount of initiator molecules in the microenvironment of the clay, resulting in a lower internal conversion rate of the excited initiator to the ground state, thus increasing the yield of the triplets and, consequently, that of free radicals. The presence of the modifying chain C16 reduces the photopolymerization rates when compared with C8. This decrease is most likely due to the C16 causing a larger increase in the interlayer than C8, enabling a higher mobility of the excited initiator. The R_p values for the nanocomposites prepared in acetonitrile were higher than when using ethanol.