The aflatoxin production by Aspergillus flavas ATCC 15517 decreased in the mixed culture with Aspergillus awamori, Aspergillus kawachii, Aspergillus niger, Aspergillus oryzae, ar with Aspergillus shirousamii to 1.3%, 13.8%, 1.3%, 0.7%, or 38.5% of that of monoculture respectively. These koji molds degraded 75∼100% of added aflatoxin B₁ (791㎍/50㎖ YES medium). A. awamori secreted during growth aflatoxin degrading factor(s) which was heat-labile. The degraded aflatoxin by the factor(s) showed no toxicity against Bacillus megaterium NRRL B-1368.