The db/db mice manifest non-alcoholic fatty liver disease. The aim of this study was to investigate the effect of Paecilomyces japonica on hepatic steatosis in db/db mice. Four-week-old male db/db mice (n=12) and their lean heterozygote littermates (db/+, n=6) were obtained. The db/db mice were fed AIN-93G diet or diet containing 3% freeze-dried P. japonica for 6 weeks after one week of adaptation period. The db/+ mice were fed AIN-93G diet. Serum alanine amininotransferase (ALT) activities and hepatic thiobarbituric acid reactive substances (TBARS) levels were measured. Liver lipids were extracted and the amounts of triglyceride were determined. Serum ALT activities were significantly higher in db/db mice than db/+ mice, whereas, these elevated activities were significantly lowered by P. japonica compared with non-treated db/db mice (p