Abstract  As a replacement for chlorofluorocarbons that cause ozone depletion, 1-bromopropane has been widely used in work place. In the present study, the formation of N-7-guanine adduct in DNA by 1-bromopropane was evaluated in vitro to elucidate the possible mechanism of its toxic action. N-7-Propyl guanine was chemically synthesized and structurally characterized by NMR, UV, HPLC, and liquid chromatographyelectrospray ionization mass spectrometry (LC- ESI MS) for using as a reference standard. An incubation of 2'-deoxyguanosine with 1-bromopropane produced N-7-propyl adduct, which was identified by UV, HPLC and ESI-MS. In addition, N-7-guanine adduct was also identified from the incorporation of calf thymus DNA with 1-bromopropane at the physiological condition by LC-ESI MS. Furthermore, the production of adduct was proportional to the amounts of 1-bromopropane used. These results indicated that the molecular mechanism underlying toxic effects of 1-bromopropane would be associated with the adduct formation on DNA at least in part.