Abstract: The ternary phase diagram of methyl methacrylate (MMA)/acrylic acid (AA)/water soap-free microemulsion system was figured out by the conventional titration technique, and the domains of different types of single phase microemulsions were partitioned with conductivity measurement.Based on the phase diagram, the influence of the amount of initiator (AIBN), the contents of AA and water on the rate of polymerization in MMA/AA/H2O soap-free inverse microemulsions was investigated.The results showed that polymerization rate increased with increasing amount of initiator or increasing content of AA and there appeared a peak value of rate with increasing content of water.The kinetic relation was obtained, which indicated that AA was an effective emulsifier to enforce and hasten polymerization in dispersed droplets at the same time with conventional polymerization in the continuous phase.In addition, the morphology of the products from soap-free microemulsion was observed under an environment scanning electron microscope and the existence of microporous structure was found.