Copolymers of aniline and o-phenylenediamine/hydrophilic bentonite nanocomposites were synthesized by 5:1 M ratios of the respective monomers with different percentages of nanoclay via modified in situ chemical copolymerization. The results were justified by measuring the FT-IR for PANI-o-PDA/bentonite nanocomposites. The thermal stability was studied. PANI-o-PDA/bentonite nanocomposites were thermally more stable than pure polymer. The antibacterial activities of PANI-o-PDA/bentonite nanocomposites towards both Gram-positive and Gram-negative bacteria were investigated. © 2013 Taylor & Francis.