In enzymology, a sterigmatocystin 8-O-methyltransferase (EC 2.1.1.110) is an enzyme that catalyzes the chemical reaction

S-adenosyl-L-methionine + sterigmatocystin ${\displaystyle \rightleftharpoons }$ S-adenosyl-L-homocysteine + 8-O-methylsterigmatocystin

Thus, the two substrates of this enzyme are S-adenosyl methionine and sterigmatocystin, whereas its two products are S-adenosylhomocysteine and 8-O-methylsterigmatocystin.

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:sterigmatocystin 8-O-methyltransferase. Other names in common use include sterigmatocystin methyltransferase, O-methyltransferase II, sterigmatocystin 7-O-methyltransferase (incorrect), S-adenosyl-L-methionine:sterigmatocystin 7-O-methyltransferase, and (incorrect).

• Bhatnagar D, McCormick SP, Lee LS, Hill RA (1987). "Identification of O-methylsterigmatocystin as an aflatoxin B1 and G1 precursor in Aspergillus parasiticus". Appl. Environ. Microbiol. 53 (5): 1028–33. PMC 203804. PMID 3111363.
• Yabe K, Ando Y, Hashimoto J, Hamasaki T (1989). "Two distinct O-methyltransferases in aflatoxin biosynthesis". Appl. Environ. Microbiol. 55 (9): 2172–7. PMC 203052. PMID 2802602.