Thermal and structural properties of three clays (sepiolite and two kaolinites) from Turkey were studied by thermal analysis (TG-DTA), X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier transform infrared (FT-IR), and surface area measurement techniques The adsorption of sulfur dioxide (SO2) gas by these clays was also investigated. SO2 adsorption values of K1, K2, and S clay samples were measured at 20 A degrees C and pressures up to 106 kPa. Sepiolite sample (S) primarily consists of pure sepiolite, only dolomite present as accompanying mineral. Both kaolinite samples, K1 and K2, mainly contain kaolinite as the major clay mineral and quartz as impurity. In K2 sample, muscovite phase is also present. Simultaneous TG-DTA curves of all clay samples were obtained at three different heating rates 10, 15, and 20 A degrees C min(-1) over the temperature range 30-1200 A degrees C. It was found that the retention value of SO2 by S clay (2.744 mmol/g) was higher than those of K1 (0.144 mmol/g) and K2 (0.164 mmol/g) samples.