According to the present invention, there is reliably provided a soy sauce having desired ethanol and lactic acid concentrations and a mellow flavor. A method of brewing soy sauce which comprises mixing soy sauce koji into a salt water to prepare a soy sauce moromi mash, adding pre-cultured soy sauce lactic acid bacteria and soy sauce yeast to the moromi mash, performing fermentation and aging of the moromi mash after adding by ordinary techniques, wherein the soy sauce yeast is added to the soy sauce moromi mash within 10 days after mixing such that the cell count of the soy sauce yeast is 10 to 100 fold greater than that of wild yeast already existing in the moromi mash and is 2.times.10.sup.5 or less cells/g moromi mash to the soy sauce moromi mash, so that the desired soy sauce is obtained.