The　non-a-position　metabolites　of　nitrosamines　play　an　important　role　in　chemical　carcinogenesis.　Ab　initio　computations　are　carried　out　to　study　the　reactivity　of　beta-　and　gamma-position　metabolites　of　methylakylnitrosamines.　Taking　N-methyl-N-nitroso-2-(sulfate)ethylamine(I),　N-methyl-N-nitroso-2-(phosphate)ethylamine(II),　N-methyl-N-nitroso-2-(glucuronate)ethylamine(RI),　N-methyl-N-nitroso-3-(sulfate)-propylamine　(IV),　N-methyl-N-nitroso3-(phosphate)propylamine(V),　and　N-methyl-N-nitroso-3-(glucuronate)propylamine　(VI)　as　models,　we　investigate　their　reactivity　with　the　anchimeric　assistant　process　of　the　N-nitroso　groups.　Full　geometric　structure　optimization　has　been　done　for　all　reactants,　intermediates　and　transition　states.　The　activation　energies,　vibrational　frequencies　and　IRC　are　also　obtained.　All　computations　are　performed　at　RBF/6-31G(d)　and　MP2/6-31G(d)　levels.　The　results　show　that　the　reactivity　of　the　sulfates　(　I　and　IV)　are　obviously　higher　than　those　of　the　phosphates　(II　and　V)　and　the　glucuronates　(III　and　VI).　And　these　data　indicate　that　the　anchimeric　assistance　is　much　more　efficient　when　the　leaving　group　is　on　the　beta-carbon　than　on　the　gamma-carbon.