A process of producing a rich-flavor soy sauce, including mixing soy sauce koji and salt water in a tank for preparing moromi mash, adding soy sauce and soy sauce koji at an appropriate point in time during the period of fermentation and aging, and subsequently effecting further aging. The process does not require any special treatment, and is quite convenient, in that it employs conventional process steps for producing a soy sauce. The resultant soy sauce has a light color and yet gives a rich flavor comparable to that of regular soy sauce, has a rich taste comparable to that of saishikomi-shoyu having a total nitrogen content of not less than 2% (W/V), and is mild in terms of saltiness.