Abstract: Standard molar enthalpies of formation of the radical compounds （CH₃S, CH₃SH, CH₃SO, CH₃SO₂） have been studied by seven density functional theory methods with the （DZP++） basis set. By carefully choosing the isodesmic reactions, the BPW91 predicted values are （-23.56 kJ/mol） （CH₃S）, 115.85 kJ/mol（CH₃SH）, -106.16 kJ/mol （CH₃SO） and （-255.56 kJ/mol） （CH₃SO₂）, respectively, which are in good agreement with the available experimental values. This shows that DFT method can provide good results using only a comparatively less amount of calculation and a modest size of basis sets. For some special case like that of （CH₃SO₂）, the predicted result is even better than values provided by the more sophisticated CCSD（T）/CBS.