Twenty different fish diets marketed in Japan were examined for the microbial flora.The total counts of aerobic bacteria determined at 30°C ranged from 1.8×103 to 8.0×105 pergram of diet with a mean value of 1.4×105. The microflora of these diets were consisted mainly of Gram-positive bacteria, and the most predominant organisms belong to the genus Bacillus and Staphylococcus. The total fungal plate counts determined at 20°C ranged from 4.0×10 to 9.6×104/g. of the diet with a mean value of 1.1×104/g. Coliform organisms were detected in 16 samples and Escherichia coli was isolated from 10 out of the 16 samples. Streptococcus were found in 4 samples. No Salmonella was detected but Vibrio was detected in 3 out of the samples. Clostridium perfringens producing lecithinase was isolated from 10 out of the 20 samples.