Glycine betaine is a widespread osmopretectant existed in many organisms. In higher plant, glycine betaine is synthesized via a two-sep oxidation reaction: choline-->betaine aldehyde-->glycine betaine. The first step, also the speed-limiting step, is catalyzed by choline monooxygenase(CMO). Choosing halophyte Atriplex hortensis as material, we constructed a salt stress-induced cDNA library, and isolated a 1.77 kb length cDNA clone with spinach CMO cDNA as probe. The sequencing result showed a complete Open Reading Frame encoding a 438-amino-acid polypeptide which was 81% and 72% identified to CMO sequences of spinach and sugar beet in amino acid homology respectively. Compared with the CMO from spinach and sugar beet, the AhCMO had one conserved Rieske-Type [2Fe-2S] cluster-binding region and one conserved mononuclear Fe-binding motif. The expression pattern of AhCMO under salt stress was also stuied, the transcriptional level of AhCMO raised about three folds after the plant was treated with brine for 4 days. The AhCMO was then transfered into tobacco(Nictiana tabacum var. Xanthi) with 35S promotor and seven transgenic plants were certified by northern blot, these plants displayed some salt- and drought-stress tolerance when grew well on MS medium contained 1.2% NaCl or 10% PEG while the control was stagnated under the same cndition.