The thermal decompositions of the 4,6-dimethyl-2-thiopyrimidine complexes Zn(DMTP)2Cl2, Cd(DMTP)2Cl2, HgDMTPCl2, Pt(DMTP)2Cl2, Pd(DMTP)2Cl2, and AuDMTPCl3 have been studied in air atmosphere by thermogravimetric and differential scanning calorimetric techniques. IR spectroscopy was used for the characterization of the intermediate and final products of the pyrolysis. The complexes show different thermal behaviours depending on the coordination mode of the DMTP ligands to the metal ions in the series of complexes studied. The enthalpies of several of the decomposition processes were calculated.