Abstract Tetrasulfur dinitride was formed by the mild pyrolysis of tetrasulfur tetranitride in the presence of a large amount of sulfur. The stoichiometric correlations of the pyrolytic products indicated a step-by-step degradation of the tetrasulfur tetranitride. Differential scanning calorimetry of an interrupted pyrolysis and determinations of the products gave the enthalpy of the formation of gaseous tetrasulfur dinitride as 351±3 kJ mol−1, which was reasonable judging from the bond enengies calculated by Sanderson’s method and those deduced from known bond energies. The obtained standard enthalpy of the formation of tetrasulfur tetranitride was 469±1 kJ mol−1, which agreed with the value reported by Barker et al.