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ABSTRACT Stimuli-sensitive hydrogels are one of the most promising and versatile materials with many potential applications. In this article, a pH-sensitive hydrogel [P(AA- co-C8PhEO10Mac)] was synthesized by the free-radical cross-linking polymerization of acrylic acid (AA) and octylphenyl polyoxyethylene methacrylate macromonomer (C8PhEO10Mac). Swelling property, swelling, and deswelling kinetics of the hydrogels in different pH media were studied and hydrogel microstructures were investigated by means of scanning electron microscopy (SEM). Theophylline was chosen as a model drug and the controlled-release properties of hydrogels were pilot studied. The results showed that the P(AA- co-C8PhEO10Mac) hydrogel has a porous structure, both the rapid swelling and deswelling rate, and good pH sensitivity characteristics; The swelling ratios of the gels in stimulated intestinal fluids (SIF, pH = 7.4) were higher than those in stimulated gastric fluids (SGF, pH = 1.4). The in vitro cumulative release data were analyzed using an empirical equation to compute the diffusion exponent ( n), whose values suggest a non-Fickian mode of transport. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1981-1989, 2013 [ABSTRACT FROM AUTHOR]