The object of the present invention is to provide a microbial mutant capable of producing S-adenosylmethionine (hereinafter referred to as SAM) in a large amount with no change in growth characteristics and a method of efficiently producing SAM by incubating the microbial mutant.The method of producing S-adenosylmethionine comprises incubating a microorganism having a loss or a reduction in the function of an enzyme relating to synthesis of phosphatidylcholine and recovering S-adenosylmethionine accumulated in the culture.