A strain designated MK107-39, producing kojic acid with a high yield, was obtained by a new screening method using a 96-well microtiter plate after NTG treatment of Aspergillus oryzae ATCC 22788. The amount of kojic acid produced by strain MK107-39 in a shaking flask was 28 g/l from 100 g/l of glucose, which was 7.7-times higher than that produced by parent strain. The kojic acid yields per cell and the amount of glucose consumed were 9.8 and 6.0-times higher than those of the parent strain. Based on differences in the use of carbohydrates and organic acids, it seems that strain MK107-39 has some mutation regarding carbohydrate metabolism. By customizing the medium and culture conditions such as glucose concentration, dissolved oxygen concentration and pH of the fermentation broth, more than 110 g/l of kojic acid was produced in a 3-l jar fermenter. Upon scale up to a 600-l pilot fermenter, enhanced production of kojic acid was successfully achieved. The kojic acid yield from glucose consumed, Y-P/S, was 0.43 (g/g) in this pilot plant-scale fermentation.