N-nitrosamine　is　a　class　of　carcinogenic,　mutagenic,　and　teratogenic　compounds,　which　can　be　produced　from　N-nitrosation　of　amine　by　nitrosating　agents.　N-nitrosation　of　19　amines　(eight　acyclic　amines,　five　heterocyclic　amines,　and　six　amines　with　unsaturated　groups)　by　N2O3　was　investigated　at　the　CBS-QB3　level　of　theory.　The　results　indicate　that　generally　the　heterocyclic　amines　have　the　highest　reactivities　among　the　three　kinds　of　amines,　whereas　the　reactivities　of　the　amines　with　unsaturated　and　electron-withdrawing　groups　are　relatively　low.　Frontier　molecular　orbital　analysis　indicates　that　the　energy　gap　between　the　HOMO　of　an　amine　and　the　LUMO　of　N2O3　has　a　close　connection　with　the　reactivity　of　an　amine.　A　structure-reactivity　relationship　of　amines　in　the　N-nitrosation　reactions　by　N2O3　was　established　using　the　stepwise　multivariate　linear　regression.　The　results　indicate　that　the　reactivity　of　an　amine　has　a　definite　relationship　(R　(adj)　(2)　=　0.947)　with　the　heterolytic　bond　dissociation　energy　of　R1R2N-H　bond,　energy　of　HOMO,　NBO　occupancy　of　the　natural　lone　pair　orbital　of　N　atom,　the　NBO　charge　of　the　N　atom,　and　the　pyramidalization　angle　of　an　amine.　This　work　will　be　helpful　to　gain　more　insight　into　the　N-nitrosation　reactions.