The mass spectrometric behavior of 1,2,4-oxadiazolyi-N-methylpyridinium salts has been investigated. These substances are of current interest as perspective ionic liquids, compounds used as green solvents for synthesis, and for their catalytic properties. The studies have been developed through electrospray ionization tandem mass spectrometry (ESI-MS/MS) experiments. The obtained results demonstrate a ready distinction between the two isomeric classes, 3-N-methylpyridinium- and 5-N-methylpyridinium-1,2,4-oxadiazoles, is possible through ESI-MS/MS experiments. A deeper investigation on the principal fragmentation pathways of characteristic ions has been also developed