The effect of particle size on curing kinetics and dynamic properties was examined with model filled rubber compounds containing monodisperse size crosslinked polystyrene (PS) particles synthesized from emulsifier-free emulsion polymerization. In the process of curing, the magnitude of the dynamic moduli increased and the gelation time (GP) decreased as PS particle diameter decreased from 1.25 to 0.315 mu m. GP was 5.5 hours for the pure matrix, 13 minutes for the composite containing 0.315 mu m particles, 1.4 hours for 0.688 mu m particles and more than 2 hours for 1.25 mu m particles. We propose that in PS particle filled systems, the ability to form clusters was due to interparticle dispersive interactions which increase with decreasing particle size. The particle clusters function as physical crosslinks, so that the overall crosslink density was significantly enhanced. Rheologically, the dynamic moduli and gelation rate were increased with decreasing particle diameter.