Enzymatic allylation of catechols was realized via catechol O-methyltransferase (COMT) using an allylated S-adenosyl-L-methionine (allyl-SAM) analog, with relatively good chemo- and regioselectivities. This new reaction offered an alternative procedure for allylation of catechols, which can be expanded as a biocatalytic allylation method in organic synthesis.