Thermal decomposition of alkali metal thiocyanates of the general formula MSCN (M=Na, K, Rb, Cs), CuSCN and AgSCN has been studied. Thermal analysis curves and diffraction patterns of the solid intermediate, and final, products of their pyrolysis are presented. Gaseous products of the decomposition, SO2 and CO2, were quantified. Thermal, X-ray and chemical analyses have been used to establish the nature of the reactions occurring at each stage of decomposition.