In enzymology, a cyclopropane-fatty-acyl-phospholipid synthase (EC 2.1.1.79) is an enzyme that catalyzes the chemical reaction

S-adenosyl-L-methionine + phospholipid olefinic fatty acid ${\displaystyle \rightleftharpoons }$ S-adenosyl-L-homocysteine + phospholipid cyclopropane fatty acid

Thus, the two substrates of this enzyme are S-adenosyl methionine and phospholipid olefinic fatty acid, whereas its two products are S-adenosylhomocysteine and phospholipid cyclopropane fatty acid.

This enzyme belongs to the family of transferases, specifically those transferring one-carbon group methyltransferases. The systematic name of this enzyme class is S-adenosyl-L-methionine:unsaturated-phospholipid methyltransferase (cyclizing). Other names in common use include cyclopropane synthetase, unsaturated-phospholipid methyltransferase, cyclopropane synthase, cyclopropane fatty acid synthase, cyclopropane fatty acid synthetase, and CFA synthase.

As of late 2007, 6 structures have been solved for this class of enzymes, with PDB accession codes 1KP9, 1KPG, 1KPH, 1KPI, 1L1E, and 1TPY.