The sterilizing effect of supercritical carbon dioxide (SC-C02) is described as compared with gaseous C02(G-C02) and liquid C02(L-C02). Baker’s yeast, Escherichia coli, Staphylococcus aureus and conidia of Aspergillus niger were sterilized by treating with SC-C02 at 200 atm and 35°C when the water content of each microorganism was 70 ~ 90%. However, dry cells with a water content of 2 ~ 10% could not be sterilized under the same conditions. No sterilizing effect from SC-C02 on endospores of Bacillus subtilis and B. s tear other mophilus was observed. G-C02 and L-C02 produced no sterilizing effect against both wet and dry baker’s yeast cells, while wet E. coli cells were sterilized with G-C02. Although dry conidia of A. niger could not be sterilized with SC-C02 alone, the addition of ethanol or acetic acid to SC-C02 made it possible to sterilize these. Without any decrease in their enzymatic activities, E. coli and baker’s yeast in α-amylase and lipase preparations were sterilized with SC-C02.