Structure of intercalated compounds of montmorillonite and 6-or 12-polyamides was studied by XRD, DSC and IR. Basal spacing was increased stepwise; 1.36nm, 1.83nm and 2.30nm. Two phases; 1.36nm/1.83nm and 1.83nm/2.30nm, were coexisted in montmorillonite/6-polyamide compounds. On the other hand, random mixed-layer phases, in which two lattice units, 1.36nm/ 1.83nm or 1.83nm/2.30nm, was randomly mixed, were observed for montmorillonite/12-polyamide compounds. When polymer contents was low, an associated NH-group with polar interaction and fusion of a polyamide were not observed in IR-absorption spectra and DSC curves. As the contents was increased, the associated NH-groups in polyamide and the fusion of polyamide were observed. Results of Fourier transformations of XRD suggested that an arrangement of polyamide chains in the interlayer spacing of montmorillonite was restricted to parallel to the silicate layers. It was concluded that the weak Van der Waals interactions between silicate surface and guest molecules played an important roll to determine a structure of the intercalated compounds.