Summary Thermo-XRD-analysis is applied to identify whether or not the adsorbed organic species penetrates into the interlayer space of the smectites mineral. In this technique an oriented smectite sample is gradually heated to temperatures above the irreversible dehydration of the clay, and after each thermal treatment is diffracted by X-ray at ambient conditions. In the thermal treatment of organo-clays, under air atmosphere at temperatures above 250°C, the organic matter is in part oxidized and charcoal is formed from the organic carbon. In inert atmosphere e.g. under vacuum above 250°C the organic matter is pyrolyzed and besides small molecules, charcoal is formed. If the adsorbed organic compound is located in the interlayer space, the charcoal is formed in that space, preventing the collapse of the clay. A basal spacing of above 1.12 nm suggests that during the adsorption the organic compound penetrated into the interlayer space. Thermo-XRD-analyses of montmorillonite complexes with anilines, fatty acids, alizarinate, protonated Congo red and of complexes of other smectites with acridine orange are described. To obtain information about spacings of the different tactoids that comprise the clay mixture, curve-fitting calculations on the X-ray diffractograms were adapted.