In enzymology, a cobalt-factor II C20-methyltransferase (EC 2.1.1.151) is an enzyme that catalyzes the chemical reaction

S-adenosyl-L-methionine + cobalt-factor II ${\displaystyle \rightleftharpoons }$ S-adenosyl-L-homocysteine + cobalt-factor III

The two substrates of this enzyme are S-adenosyl methionine and cobalt-factor II; its two products are S-adenosylhomocysteine and cobalt-factor III.

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:cobalt-factor-II C20-methyltransferase. This enzyme is also called CbiL. This enzyme is part of the biosynthetic pathway to cobalamin (vitamin B₁₂) in anaerobic bacteria such as Salmonella typhimurium and Bacillus megaterium.