Myocarditis has been reported in male F344 rats given a diet containing hinokitiol (HT). A subchronic toxicity study was here performed to re-evaluate toxic effects of HT in both sexes of F344 rats with dietary administration at concentrations of 0%, 0.02%, 0.07% and 0.2% for 13 weeks. Significant reduction of body weight gain was noted in 0.2% males and 0.07% and above females. Significant decrease in RBC counts, hemoglobin and hematocrit was detected in 0.07% and 0.2% females. Significant increase in MCV was observed in 0.07% and above males and 0.2% females. In the rats given 0.07% and 0.2%, significant increase in total protein and albumin were detected in males, and in total cholesterol in females. Significant increases in total cholesterol, urea nitrogen and creatinine were also detected in the 0.2% males. Significant increase in relative liver weights was detected in the 0.07% and above males and females. Absolute and relative heart weights were significantly decreased in the 0.07% and above males. Based on the above findings the no-observed-adverse-effect level (NOAEL) of HT for both male and female rats was estimated to be 0.02%, translating into 12.7 and 14.8 mg/kg b.w./day, respectively. Myocarditis was not evident in the present study.