The bentonite deposits in Başören Kütahya, W Anatolia, Turkey were formed by alteration of Pliocene perlite and pyroclastic rocks. Two types of bentonites are distinguished in this area on the basis of their physical properties, chemistry and occurrence. Bentonites were examined to determine their mineralogical, chemical and physical properties. Analytical methods include X-ray diffraction (XRD), scanning electron microscopy (SEM), chemical analysis and measurement of cation exchange capacity (CEC), swelling volume, water adsorption, bleaching capacity, and firing shrinkage. Bentonites consist mainly of dioctahedral smectite. They also contain zeolite, opal-CT, cristobalite, quartz, feldspar, dolomite and calcite. The 'Type 2' bentonites had greater CEC, swelling volume, water adsorption and bleaching capacity than 'Type 1'. The variation in the physical properties of the two bentonites is attributed to the differences in the non-clay mineralogy and to the chemical composition and nature of interlayer cation.