The results of an experimental study of the thermal decomposition of tar formed in sawdust pyrolysis are discussed. The study was performed under static isothermal conditions at temperatures 500, 600, 700 and 850°C using a laboratory reactor.The reactor is equipped with an electrical heater, which allows heating of the studied tar samples up to 1273  °C. The reactor consists of a reaction chamber made as a stainless steel cylinder with a diameter of 2 cm and a height of 10 cm.The temperature in the reaction chamber was recorded using a thermocouple and a temperature meter-controller «Pine-002», providing the measurement of temperatures up to 1273 °C with the accuracy of ± 0,01  °C.Samples of the tar produced at the pyrolysis of sawdust at 450  °C were installed into a quartz vessel and kept in the reaction chamber until they reached constant weight. This required about 60 minutes at 500  °C and about 5 minutes at 850°C and is a result of a homogeneous decomposition of tar. The initial weight of tar samples was about 1.5 gram. The change in their weights was determined at regular time intervals using the Stoll electronic balance with a relative error of 2%.On the basis of the performed studies it was found that the apparent activation energy of a homogeneous decomposition of tar is equal to approximately 63.1 kJ/mol.It was found as well that the rate of tar decomposition increased when samples of natural Belarusian dolomites were placed into the reaction zone . This increase is due to the occurrence of a heterogeneous catalytic reaction of tar decomposition. The apparent activation energy of this process was determined to be equal to 57.2 kJ /mol which is consistent with estimations of other researchers.The conclusion about the prospects of natural dolomite Belarus as catalysts of thermal decomposition of heavy hydrocarbons generated during the thermochemical conversion of biomass has been drawn on the basis of the established results.