Sterol C24-methyltransferase(SMT) plays multiple important roles in plant growth and development. SMT1, which belongs to the family of transferases and transforms cycloartenol into 24-methylene cycloartenol, is involved in the biosynthesis of 24-methyl sterols. Here, we report the cloning and characterization of a cDNA encoding a sterol C24-methyltransferase from Tripterygium wilfordii(Tw SMT1). Tw SMT1(Gen Bank access number KU885950) is a 1530 bp cDNA with a 1041 bp open reading frame predicted to encode a 346-amino acid, 38.62 k Da protein. The polypeptide encoded by the SMT1 cDNA was expressed and purified as a recombinant protein from Escherichia coli(E. coli) and showed SMT activity. The expression of Tw SMT1 was highly up-regulated in T. wilfordii cell suspension cultures treated with methyl jasmonate(Me JA). Tissue expression pattern analysis showed higher expression in the phellem layer compared to the other four organs(leaf, stem, xylem and phloem), which is about ten times that of the lowest expression in leaf. The results are meaningful for the study of sterolbiosynthesis of T. wilfordii and will further lay the foundations for the research in regulating both the content of other main compounds and growth and development of T. wilfordii. Sterol C24-methyltransferase (SMT) plays multiple important roles in plant growth and development. SMT1, which belongs to the family of transferases and transforms cycloartenol into 24-methylene cycloartenol, is involved in the biosynthesis of 24-methyl sterols. Here, we report the cloning and characterization of a cDNA encoding a sterol C24-methyltransferase from Tripterygium wilfordii (Tw SMT1). Tw SMT1 (Gen Bank access number KU885950) is a 1530 bp cDNA with a 1041 bp open reading frame predicted to encode a 346-amino acid , 38.62 kDa protein. The polypeptide encoded by the SMT1 cDNA was expressed and purified as a recombinant protein from Escherichia coli (E. Coli) and showed SMT activity. The expression of Tw SMT1 was highly up-regulated in T. wilfordii cell suspension cultures treated with methyl jasmonate (Me JA). Tissue expression pattern analysis showed higher expression in the phellem layer compared to the other four organs (leaf, stem, xylem and phloem), which is about ten times t hat of the lowest expression in leaf. The results are meaningful for the study of sterol biosynthesis of T. wilfordii and will further lay the foundations for the research in regulating both the content of other main compounds and growth and development of T. wilfordii.