Taking the leaves of Ampelopsis grossedentata as cDNA template, we amplified amyrin synthase gene by the method of RTPCR to study the triterpenoid biosynthesis. It was named AgAS. The results demonstrated that the AgAS gene was 2250 bp in length and coded 750 amino acids, showing a closest relationship of homologous protein with Vitis vinifera L.. When fused to green fluorescent protein(GFP), AgAS gene mainly localized to the nucleus and cell membrane. The results of Southern blot showed that there were two copies of AgAS in the genome of A. grossedentata. The expression of AgAS in different tissues and organs of two species of A. grossedentata was detected by the method of qRTPCR. The results indicated that the AgAS gene expressed in leaves, stems and roots as for purple bud A. grossedentata. Specially, the expression of leaves ranked the first, followed by stems and the roots had the lowest expression. With the maturity of leaves, the expression increased at first but then showed a decreasing trend. Whereas for the green bud A. grossedentata, the expression of AgAS gene showed an increasing trend with the maturity of leaves, and the expression was relatively low in roots and stems.