The poly(methylacrylic acid) modified by silane [poly(methylacrylic acid-co-vinyl triethoxylsilane) (PMAA)] was prepared via free-radical polymerization with different mass ratios of methylacrylic acid to vinyl triethoxylsilane (VTES). The swelling performance of the prepared PMAA in different solutions with various pH values, salt species (NaCl and CaCl2), and concentrations was investigated in detail. The results indicated that the introduction of silane boosted the stability of the obtained PMAA in aqueous solutions in the presence of an increased quantity of VTES additive. Meanwhile, the different swelling ratios of PMAA in various pH solutions showed a high pH responsivity. In addition, we found that when the PMAA underwent a number of swelling–deswelling cycles, it demonstrated the good reversibility properties when the pH value of the swelling medium was changed from 9.0 to 1.4. Moreover, the swelling mechanism of PMAA in different solutions with different pH values was investigated. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40403.