The features of tritium adsorption by clay rocks, which mainly consist of clay minerals with high adsorption abilities for tritium oxide (НTO) and super heavy water (T2O), were studied after their thermal treatment at a temperature of 105 and 500 °C. The observation was carried out in a closed system "tritiated water - clay rock". Indicators of the dynamics of growth of tritium adsorption by heat-treated clay rocks over 380 days are obtained. It was found that the adsorption of tritium in this observation system actively grows for the first 30 - 40 days for all the studied minerals, and then slows down. White clays retain an increase in adsorption over the entire observation period of 380 days.