Abstract: The fragmentation characteristic of a series of recently developed 2-amino-5-substituted-4-thiazolyl-phosphonates is studied by using electron impact (EI), electron impact-collision activity-mass analysed ion kinetic energy spectrometry (EI-CA-MIKES) and accurate mass measurment (AMM) techniques.It is found that a new type of γ-alkyl rearrangement has occured as evidenced by the'pres-ence of a molecular daughter ion of ethylated thiazole ring(m/z 203).The molecular parent and daughter ions have been fully identified by their unsaturation, accurate ion mass and elementary constitution.The fragmentation pathway is portrayed in a scheme(see Fig.2)

Key words: γ-Alkyl rearrangment, EI-CA-MIKES, Thiazolyl, Phosphonate