In enzymology, a pinosylvin synthase () is an enzyme that catalyzes the chemical reaction
Thus, the two substrates of this enzyme are malonyl-CoA and cinnamoyl-CoA, whereas its 3 products are CoA, pinosylvin, and CO<sub>2</sub>.
This enzyme belongs to the family of transferases, specifically those acyltransferases transferring groups other than aminoacyl groups. The systematic name of this enzyme class is malonyl-CoA:cinnamoyl-CoA malonyltransferase (cyclizing). Other names in common use include stilbene synthase, and pine stilbene synthase. This enzyme participates in phenylpropanoid biosynthesis.