Inverse dispersion polymerizations of acrylic acid were conducted by using a water-soluble redox initiation system under both isothermal and nonisothermal conditions. The polymerizations were monitored by measuring residual monomer by highperformance liquid chromatography for isothermal polymerizations or by monitoring the temperature variation inside the dispersion for nonisothermal polymerizations. The aqueous drop behavior was examined throughout the course of polymerization by scanning electron microscopy with freeze-fracture equipment. The agitation intensity had a significant effect on polymerization, drop size, and distribution. The volume of aqueous reductant affected the polymerization rate End limiting conversion. A second shot of aqueous reductant induced a further initiation of reaction. The rate of dispersion polymerization was slower than that of solution polymerization with surfactant. A hypothesis was proposed that :polymerization occurred in aqueous drops. Coalescence and breakup of aqueous drops took place simultaneously and played an important role in polymerization.