Abstract: The mass spectra of sixteen 1-substituted 5-trinuoromethy-limidasole-4-phospho-nated (1～8) and-4-carboxylates (9～16) are reported. The fragmentation pathways have been studied usinghigh resotution mass spectrometry and metastable ions measure-ments. The spectra of compouns 1～8 exhibit molecular ion peaks of low intensity. For spectra of compounds 9 ～16 pronounced molecular ion peaks were observed. A rear-rangement involving C2H5 and C2H4 tranfer from oxygen atom to nitrogen and carbon atom of imidazole cycle for compounds 1～8 are described.