The polyphenol oxidase (PPO) was found to positively regulate the accumulation of salvianolic acid B (SAB). This investigation further clone its cDNA sequence from hairy roots of Salvia miltiorrhiza by using RACE technique (named as SmPPO, GenBank accession No. KF712274). The full length cDNA of SmPPO was 1 930 bp with a 1 770 bp open reading frame, encoding a protein of 589 amino acids. Two Nglycosylation sites were found in Nterminus thylakoid transfer domain, when comparing the amino acid sequences of SmPPO to other PPOs in Tubiflorae. Expression analysis of realtime PCR indicated that PPO transcript levels significantly increased in yeast extract (YE)elicited hairy roots, whereas it significantly decreased in the Ag⁺, ascorbic acid and cysteine treatments. Correspondingly, the accumulation of SAB was significantly increased in YEtreatment hairy roots, and was inhibited by the three elicitor treatments. These results suggest that SmPPO gene positively regulates the accumulation of SAB.