Kona-koji was prepared without the addition of a koji starter (Tanc-koji) for the production of Imo-shochu. The spores of molds carried in the air affected growth during the preparation of koji. So, we isolated the spores of molds from the vicinity of the places used for the preparation of koji and production of shochu. As shown by the results, a 103 order of colonies per gram·koji of A. oryzae were isolated from kojimuro solids, shochu distillery solids and from the leaves of N. antiqua that are used to wrap the koji A. oryzae spores were also isolated from the air of the koji-muro and shochu distillery. In addition spores of A. niger and other molds were also isolated. We measured the enzyme activity of these strains and investigated their physiological characteristics. Their acidity was higher than that of the standard strains. The characteristics of these strains agreed with those of strains isolated from kona-koji. Therefore, we found that spores of Aspergillus sp. were mixed with the raw material for koji from the leaves of N. antiqua or airborne spores, and these spores grew during the preparation of koji. Further more, spores of other mold contaminating koji were isolated from the leaves of N. antiqua, but they were not detected in the koji. We found that their mold were selected against as the temperature of koji rose to 40C during its preparation.