In this study, we prepared pH-sensitive hydrogel microspheres by means of atom transfer radical polymerization of hydroxyethyl methacrylate and 4-vinylpyridine in inverse emulsion, using poly(ethylene glycol) dimethylacrylate as a crosslinker. One-factor experiment was used to optimize conditions of preparing microspheres and the resulting conditions were presented. The microspheres were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis, scanning electron microscopy, and so forth. The swelling behavior of the as-prepared microspheres was studied by a classic gravimetric method. Afterward, daidzein was used as a model drug and related release mechanism was investigated. The diffusional coefficients and the corresponding kinetic parameters of chosen mathematical models for fitting drug release were calculated, which indicated drug release accorded with anomalous (non-Fickian) diffusion mechanism. (C) 2015 Society of Plastics Engineers