The manufacture of riboflavine fortified Dwen-Jang has been tried with an exceedingly riboflavine productive Aspergillus oryzae #612 mutant which has been developed by the authors. Both the rice and barley koji of this mutant and Aspergillus sojae have been prepared. Their riboflavine production, saccharifying and protease activities have begin compared The riboflavine fortified Dwen-Jang has been manufactured using the barley koji of riboflavine productive mutant. Their riboflavine content and qualities have been studied comparing with an ordinary Dwen-Jang which has been prepared with the barley kojo of A. sojae strain. The following results have been obtained. (1) The baley koji was superior in riboflavine production and protease activity, inferior in saccharifying ability than rice koji both with A. oryzae #612 and A. sojae. (2) In barley koji, the mutant, A. oryzae #612, produces 1.5 times riboflavine than A. sojae and shows stronger saccharifying and protease activities than the latter. (3) The riboflavine fortified Dwen-Jaug manufactured contained $5.2{gamma}/g$ of riboflavine, about 1.5 times that of A. sojae. The higher contents of free sugar and free amjno nitrogen have been observed than the ordinary Dwen-Jang manufactured with A. sojae.