The composite gels were prepared by adding bentonite or its acid-activated derivative into the carboxylmethylcellulose (CMC) gel, and the resulted products were characterized with infrared spectroscopy. Different from ordinary swellable hydrogels, the CMC/bentonite hydrogel beads shrinked in water. The water sorption of dried gels was limited below 120% of their own weight, and a sorption equilibrium reached quickly within 20-40 min. The water of swollen gels exists mainly in bound status according to the DSC analysis. The release experiments in water were carried out to evaluate the release of herbicide metolachlor from gel formulations. The release mechanism dominated by a Fickian diffusion might be related to the quick and limited swelling of dried gels. Addition of bentonites in CMC gel is beneficial for slowing the release of metolachlor, especially when the acid-activated bentonite was added. The time taken for 50% of metolachlor to be released, t(50) was prolonged to 158 h for the composite gel formulation based on acid-activated bentonite from the 61.1 h for pore CMC gel formulation. (c) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 112: 261-268, 2009