Acetyl-CoA C-acetyltransferase (AACT) is the first enzyme in the terpene synthesis pathway, catalyzed two units of acetyl-CoA to acetoacetyl-CoA. In order to study the tanshinone biosynthesis in Salvia miltiorrhiza, a novel AACT gene, SmAACT, was cloned using cDNA microarray and RACE strategy. The full length cDNA of SmAACT is 1 623 bp (accession No. EF635969), which contained a 1 200 bp open reading frame (ORF) encoding a 399 amino acid protein. Nine introns were found in the genomic sequence. SmAACT was upregulated by YE and Ag+ elicitors both with cDNA microarray and quantitative RT-PCR analyses along with the accumulation of tanshinones. Sequence homology comparison and phylogenetic analysis all suggested that SmAACT belonged to the class of acetyl-CoA C-acetyltransferase. The transcription level of SmAACT was relatively higher in root than that in stem and leaf tissues. SNP analysis revealed that SmAACT was highly variable in the region of 6 to 9 introns with 33 SNPs in the 600 bp region, there are 5 SNPs in the cDNA region while they are all synonymous cSNPs. Some special genotypes were found in Salvia miltiorrhiza from different areas. SmAACT will be an useful gene for further analyze the mechanism of gene regulation among the tanshinones biosynthesis.