Neutral methyl cellulose (MC) was transformed into carboxylated methyl cellulose (CLMC) via the esterification reaction between MC and maleic anhydride. FTIR, X-ray diffraction, and thermogravimetry analysis results indicated the carboxyl groups were successfully incorporated onto the chains of MC. The carboxyl group percentages of CLMC ranged from 6.5 to 13.6%. CLMC and poly(vinyl alcohol) were mixed in aqueous solution, and then formed physical composite hydrogel. The equilibrium swelling ratios of the hydrogels in buffer solutions of pH 10 and 1.5 were 10.7 and 7.5, 7.7 and 6.0, 6.5 and 5.2 when the ratio of CLMC/PVA was 5 : 5, 4 : 6, and 3 : 7, respectively. The hydrogel exhibited both temperature- and pH-sensitive swelling properties, which implied not only the inherent temperature sensitive property of MC was retained but also one more function was acquired. The maximum cumulative release percentages of Rhodamine B from the CLMC/PVA (3 : 7) hydrogel in the mediums of pH 7.4 and 1.2 were 43.36 and 37.44%, respectively. Such a pH-responsive release behavior also confirmed that CLMC was anionic. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013