Abstract Crystals of 1,2,3,4,6,7-hexathia-5,8-diazocine (1,4-S6(NH)2) were transformed around 363 K with a molar enthalpy change of the transformation of 2.40±0.07 kJ mol−1. Crystal systems of the two forms of 1,4-S6(NH)2 were identified to be orthorhombic (α-form) and monoclinic (β-form) below and above this temperature. Molar heat capacities of the α- and β-forms were also deduced as being 0.1950±0.001 and 0.199±0.001 kJ mol−1 K−1 at 298.15 K, respectively. The 1,4-S6(NH)2 was pyrolyzed around its apparent melting point (405 K), producing tetrasulfur tetranitride (S4N4) and tetrasulfur dinitride (S4N2) as solid intermediates, which finally decomposed into sulfur, nitrogen, and ammonia under an argon atmosphere. A stoichiometric correlation among the final products gave an overall pyrolytic equation: 1,4-S6(NH)2=3⁄4S8+2⁄3N2+2⁄3NH3. The standard enthalpy of the formation of α-form 1,4-S6(NH)2 was estimated as being 158±2 kJ mol−1 according to the observed enthalpy changes of the pyrolysis and transformation, which reasonably agreed with that calculated.