Novel CA modified starch–CMC–MMT bionanocomposite films were prepared and the effect of MMT on the structural and physi- cal properties of the starch–CMC biocomposites was studied. An increment in the interlayer distance of the clay sheets in the bionanocomposites was observed by X-ray diffraction providing evidence that the clay nanolayer formed an intercalated struc- ture without reach a complete exfoliation. But there was no any sharp d0 0 1 peak in XRD pattern of pure starch–MMT nanocompos- ites. This result confirms the extensive diffusion of polymer chains inside galleries of clay. At the level of 7% MMT, bionanocompos- ite films showed the lowest solubility (7.21%). By addition of 3 and 7% MMT, the moisture absorption of the films decreased from 23.46% to 20.00 and 14.78%, respectively. Furthermore, MMT also demonstrated an important influence on the mechanical proper- ties. Increasing MMT content from 0 to 7% (w/w), could increase UTS from 9.83 to 27.55MPa. However, the SB decreased signifi- cantly (p≤0.05) from 63.52 to 18.25%. The temperature position of the melting peak increased from 221.5 to 243.0 ◦ C as MMT content increased from 1 to 7% (w/w) starch. By increasing of