The　mass　spectrometric　characteristics　of　N-methyl-N-nitrosourea　(MNU)　and　N-ethyl-N-nitrosourea　(ENU)　were　investigated　by　electrospray　ion　trap　mass　spectrometry　in　a　multi-stage　MS　full　scan　mode.　The　mass　spectra　were　interpreted　according　to　the　fragments　of　these　compounds　and　their　fragmentation　patterns　were　proposed.　The　results　showed　that　the　strong　[M+H]+　ion　cluster　was　obtained　in　the　positive　mode　when　the　sample　dissolved　in　acetonitrile.　During　the　process　of　collision　induced　dissociation,　they　underwent　the　neutral　loss　of　NO　and　HOCN.　These　characteristics　can　be　applied　further　to　the　elucidation　of　the　fragmentation　pathways.　©　2008　IEEE.