Although the kinetics of the precipitation polymerization of acrylic acid were investigated by a number of researchers, no mechanism has been proposed which considers the reaction in both continuous and dispersed phases. In this article a general mechanism is developed for the precipitation polymerization of acrylic acid in toluene. It is compared with experimental data and is found to predict rate of polymerization and molecular weight reasonably well. The mechanism consists of the initiation, propagation, transfer and termination reaction, which are common to all free-radical polymerizations. It also found that monomer-enhanced decomposition and transfer to monomer are the dominant mechanism for initiation and chain termination, respectively. The kinetic parameters were evaluated against experimental data.