A series of N,O-carboxy methyl-chitosan/montmorillonite (N,O-CMC-MMT) nanocomposites were prepared by controlling the molar ratios of N,O-carboxymethyl-chitosan (N,O-CMC) and montmorillonite (MMT). The nanocomposites were characterized by MR, XRD and SEM. Adsorption of Congo red (CR) anionic dye from aqueous solution onto N,O-CMC-MMT was studied. The results showed that the nanocomposite with the molar ratio of N,O-CMC to MMT of 5:1 exhibited the higher adsorption capacity. This may be attributed to the fact that the introduction of N,O-CMC in the galleries of MMT may have different influences on physico-chemical properties of MMT and in turn result in different influences on adsorption capacity of N,O-CMC-MMT for CR. The effects of different molar ratios of N,O-CMC and MMT, initial pH value of the dye solution and temperature on adsorption capacities of samples for CR dye have been investigated. The results of adsorption behaviors of CR on N,O-CMC-MMT indicated that all the adsorption processes followed the pseudo-second-order and the Langmuir isotherm, respectively. (C) 2007 Elsevier B.V. All rights reserved.