It has been shown that the reaction rate of the thermal decomposition of acid tar containing sulfoacids obeys the equation of the first order reaction. Two temperature ranges of thermal decomposition have been detected. The processes of the liquid phase transformation of the components of the reaction mixture dominate in the low temperature range (200-360A degrees C, apparent activation energy E = 37 kJ/mol), and gas-phase reactions dominate in the high temperature range (390-500A degrees C, E = 106 kJ/mol). Sulfuric acid, additionally introduced into acid tar, participates in redox reactions, resulting in the rapid formation of sulfur(IV) oxides and benzene.