Abstract: The dissociation chemistry of the protonated S-methyl benzenylmethylenehydrazine dithiocarboxylate, PhCH＝N-NHC(＝S)SCH₃ was investigated by CID-MS experiments in combination with density functional theory(DFT) calculations. Eliminations of H₂S, CH₃SH and(NSC)SCH₃ were the three main fragmentation reactions. Calculated results show that thiocarbamide sulfur is the most favored position for protonation. Both the added proton and the thiocarbamide hydrogen shift in turn to the fragment ion in the process of losing(NSC)SCH₃. The thiocarbamide hydrogen migrates to thiocarbamide sulfur concomitantly with H₂S elimination. In the case of CH₃SH elimination, one of the proton/ the thiocarbamide hydrogen migrates to the fragment ion, and the other to the neutral specie. These results indicate that fragmentation of the protonated molecule is viewed as a result of the coordinated migration of both the external proton and the thiocarbamide hydrogen.