A full length cDNA of cycloartenol synthase gene (SmCAS) was cloned from Salvia miltiorrhiza Bunge.We analyzed the sequence and structure characteristics of its encoded protein,and its expression patterns in the different organism and under different stress by quantitative RT-PCR.The full length cDNA is 2 346 bp,which includes 2 271 bp ORF and encodes 756 amino acid residues with a putative molecular mass of 86.16 kD.SmCAS has a typical conserved DCTAE motif and QW motif of oxidosqualene cyclase.Bioinformatics analysis showed that SmCAS had 83%,84%,83%,81% and 80% similarity with P.notoginseng,P.ginseng,C.asiatica,G.glabra and Arabidopsis thaliana,respectively.SmCAS expressed significantly in different tissues and had the highest transcript profile in flowers.It could be positive induced by ABA,lower temperature and drought,while its expression was inhibited by MeJA.