Abstract: Infrared spectra, differential thermal analysis curves and thermogravimetry curves of the bis-thiourea gold (Ⅰ) complex have been measured. In the heating process of the complex, the infrared spectra of the solid products of heat decomposition of the complex at 21 different selected temperatures have been measured, and the mechanism of heat decomposition was infered. The apparent activation energy and the preexponential constant of heat decomposition reaction were evaluated. At the heating rate of 10℃/min and in the range 230-260℃, thiou-rea in the ligand isomerizes into isoammonium thiocyanate. The decomposition of complex starts at 240℃ and ends at 322℃. Au₂S decomposes into the metal Au above 650℃.