Abstract Chitosan–clay biocomposites have been prepared in which KSF‐montmorillonite (KSF) is used as filler and diluted acetic acid is used as solvent for dissolving and dispersing chitosan and montmorillonite, respectively. The effect of KSF loadings in biocomposites has been investigated. The characterization with different methods (FTIR, DSC, TGA, SEM, and XRD) on chitosan/KSF biocomposites systems was examined. Morphology and properties of chitosan biocomposites have been studied compared with those of pure chitosan. The FTIR and SEM results indicated the formation of an intercalated‐and‐exfoliated structure at low KSF content and an intercalated‐and‐flocculated structure at high KSF content. The thermal stability and the mechanical properties of the composites were also examined by DSC, TGA/DTG, and tensile strength measurements, respectively. The dispersed clay improves the thermal stability of the matrix systematically with the increase of clay loading. Tensile strength of a chitosan film was enhanced until the clay ratio up to 2 wt% and elongation‐at break decreased with addition of clay into the chitosan matrix. The XRD results confirmed the intercalation of the biopolymer in the clay interlayer by the decrease of 2 θ values while the chitosan–clayratio increases. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers