The global potential energy surface (PES) of the [CH3,N,C,S] system in singlet and triplet states, involving 16 isomers and 15 transition structures, is studied at DFT(B3LYP), MP2 and QCISD levels. It is shown that the chainlike singlet isomer CH3NCS is the most stable species among all the isomers and the branched-C(CH3)NS has the lowest energy among the triplet species. The stability of these isomers, their isomerizations and dissociations are discussed and theoretical results are consistent with the available experimental ones. (c) 2006 Elsevier B.V. All rights reserved.