Primary radical (PR) desorption in the miniemulsion polymerization initiated by oil-soluble initiator was investigated. Both the aqueous phase inhibition experiments and the theoretical predictions, which combined the two film theory and aqueous phase mass balance, were performed to evaluate the PR desorption process quantitatively. The theoretical predictions agreed well with the experiment results. It was found that the organic phase diffusion, particle size, surfactant layer, aqueous phase resistance, and different initiator type affected the PR desorption. The desorption rate of PR was faster than its reaction rate at the early stage of polymerization, while the former decreased to a comparable level as the latter at the high conversion. PR was prone to desorb in the polymerization and the desorption of PR played a critical role in the miniemulsion polymerization initiated by oil-soluble initiator. It is concluded that the PR desorption-reabsorption is a process to generate effective radicals in the miniemulsion polymerization initiated by oil-soluble initiator. (C) 2014 American Institute of Chemical Engineers