Nanocomposites of bentonite with polyaniline (PANI), poly(methacrylic acid) (PMAA), and poly (aniline-co-methacrylic acid) (PANI-co-PMAA) were prepared by in situ intercalative polymerization technique. The nanocomposites were characterized by FTIR and UV-visible spectroscopies, XRD, SEM, TEM, as well as TG-DTA studies. The in situ intercalative polymerization of PANI, PMAA, and PANI-co-PMAA within bentonite layers was confirmed by FTIR, XRD, SEM, as well as TEM studies. XRD confirmed the intercalation of polymers and copolymer in bentonite. The average particle size of the nanocomposites was found to be in the range of 250-500 nm. The thermal stability was found be the highest for PANI-co-PMAA-bentonite. The swelling behavior studies suggest that these nanocomposites hold potential for their utilization in absorption of toxic materials from waste water. (c) 2006 Wiley Periodicals, Inc.