In enzymology, a mycocerosate synthase (EC 2.3.1.111) is an enzyme that catalyzes the chemical reaction

acyl-CoA + n methylmalonyl-CoA + 2n NADPH + 2n H⁺ ${\displaystyle \rightleftharpoons }$ multi-methyl-branched acyl-CoA + n CoA + n CO₂ + 2n NADP⁺

The 4 substrates of this enzyme are acyl-CoA, methylmalonyl-CoA, NADPH, and H⁺, whereas its 4 products are multi-methyl-branched acyl-CoA, CoA, CO₂, and NADP⁺.

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 acyl-CoA:methylmalonyl-CoA C-acyltransferase (decarboxylating, oxoacyl- and enoyl-reducing). This enzyme is also called mycocerosic acid synthase.