Five soil profiles developed from Botucatu Sandstone were selected for a study of the occurrence of montmorillonite. These were, respectively, two Regosols (P1 and P2), two Red-Yellow Podzolic-Laras variation (P3 and P4) and an Intergrade Regosol (P5). A total of 33 samples were taken from these profiles. Particle size distribution and routine chemical characterization was done for all samples. The clay fraction of each sample was submitted to the following analysis: determination of %K2O, silica, alluminum, cation exchange capacity, X-ray diffraction and DTA. Kaolinite was the dominant clay mineral in the soil profiles overlying unconsolidated rock material (P1 and P2) whereas montmorillonite was dominant in those overlying consolidated rock (P3, P4 and P5). Average content of montmorillonite in the Red-Yellow Podzolic profiles overlying stratified sandstone was 35%, whereas for the Intergrade Regosol the average was 57%. The results obtained indicate that montmorillonite is an inherited character in these soils. Profiles P1 and P2 are probably derived from materials other than Botucatu Sandstone.