EI-MS spectra of ten derivaties 3-(7H- 1 ,2,4-triazolo[3,4-b]- 1,3,4-thiadiazin-6-yl)coumarines were recorded and interpreted. The results shown that molecular ions of the compounds are enough stable. The relation between the structure of the molecules and the mechanism of the fragmentation in the ionization of the molecules is explained.