Novel citric acid (CA) modified starch–carboxymethyl cellulose (CMC)–montmorillonite (MMT) bio- nanocomposite films were prepared by casting method. X-ray diffraction (XRD) test showed that the 0 0 1 diffraction peak of nanoclay was shifted to lower angles in the bionanocomposites and it may be implied that the clay nanolayers formed an intercalated structure. However, completely exfoliated struc- ture formed only in the pure starch–MMT nanocomposites (without CA and CMC). At the level of 7% MMT, the composite films showed the lowest solubility (7.21%). The MMT addition at content of 7% (w/w), caused to increase in ultimate tensile strength (UTS) by more than threefold in comparison to starch–CMC biocomposites.