Aspergillus oryzae KACC 40247 was selected from among 60 fungal strains as an effective 7,8,4'-trihydroxyisoflavone (8-hydroxydaidzein)-producing fungus. The optimal culture conditions for production by this strain in a 7-L fermentor were found to be 30 °C, pH 6, and 300 rpm. Under these conditions, A. oryzae KACC 40247 produced 62 mg/L of 8-hydroxydaidzein from soybean extract in 30 h, with a productivity of 2.1 mg/L/h. These are the highest production and productivity for 8-hydroxydaidzein ever reported. To increase production, several concentrations of daidzin and of daidzein as precursor were added at several culture times. The optimal addition time and concentration for daidzin were 12 h and 1,248 mg/L, and those for daidzein were 12 h and 254 mg/L respectively. Maximum production and productivity for 8-hydroxydaidzein with the addition of daidzein were 95 mg/L and 3.2 mg/L/h respectively, and those with the addition of daidzin were 160 mg/L and 4.4 mg/L/h respectively.