In enzymology, a cycloartenol 24-C-methyltransferase (EC 2.1.1.142) is an enzyme that catalyzes the chemical reaction

S-adenosyl-L-methionine + cycloartenol ${\displaystyle \rightleftharpoons }$ S-adenosyl-L-homocysteine + (24R)-24-methylcycloart-25-en-3beta-ol

Thus, the two substrates of this enzyme are S-adenosyl methionine and cycloartenol, whereas its two products are S-adenosylhomocysteine and (24R)-24-methylcycloart-25-en-3beta-ol.

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:cycloartenol 24-C-methyltransferase. This enzyme is also called sterol C-methyltransferase.

• Mangla AT, Nes WD (2000). "Sterol C-methyl transferase from Prototheca wickerhamii mechanism, sterol specificity and inhibition". Bioorg. Med. Chem. 8 (5): 925–36. doi:10.1016/S0968-0896(00)00040-7. PMID 10882005.