Three complexes of formula (HB)(2)[M(dto)(2)] where HB+ is pyridinium, M is Ni(II), Pd(II) or Pt(II), and dto(2-) is 1,2-dithiooxalato-S,S’ (hereafter abbreviated as NIDTPY, PDDTPY and PTDTPY, respectively) have been synthesized and characterized by elemental analysis, IR and UV-vis spectroscopies and X-ray diffraction techniques. Thermal decompositions of compounds have been studied by thermogravimetry (TG and DTG) and differential thermal analysis (DTA) under argon-oxygen and argon atmospheres. The final decomposition products were identified by elemental analysis and the X-ray powder diffraction technique. Thermoanalytical data show that the surrounding atmosphere influences the course of the decomposition process, and the final products. In argon-oxygen atmosphere, the final residues were identified as a mixture of nickel sulphides, oxides and sulphate for the nickel compound, Pd(0) and PdO for the palladium compound, and platinum(0) for the platinum compound. Thermal decompositions in argon atmosphere yielded nickel(II) sulphide, a mixture of Pd/PdS, and metallic platinum, respectively.