Abstract: To investigate the fragmentation behaviors of two compounds containing carbamate group by collision induced dissociation(CID). Both electrospray ionzation-ion trap mass spectrometry and electrospray ionization-Fourier transform ion cyclotron resonance mass spectrometry were used to analyze the compounds. The samples were infused into the ion source with a syringe pump and the experiments were carried out in the positive ion mode. The most abundant fragment ion in MS2 spectrum was M+H-44+ ion. The accurate masses of the fragment ions suggested that the loss of 44u corresponded to the loss of CO 2. The same phenomenon was also observed in the CID analysis of other five compounds containing carbamate group. The neutral loss involving the cleavage of two bonds suggested an unusual rearrangement process. A mechanism for the loss of CO 2 has been proposed.