In enzymology, a pinosylvin synthase (EC 2.3.1.146) is an enzyme that catalyzes the chemical reaction

3 malonyl-CoA + cinnamoyl-CoA ${\displaystyle \rightleftharpoons }$ 4 CoA + pinosylvin + 4 CO₂

Thus, the two substrates of this enzyme are malonyl-CoA and cinnamoyl-CoA, whereas its 3 products are CoA, pinosylvin, and CO₂.^[1]

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.^[2] This enzyme participates in phenylpropanoid biosynthesis.^[2]