Dietary supplements have become very popular worldwide because they are believed to be safe with few side effects. Here, we report three cases of liver injury caused by Sennomotokounou, a Chinese dietary supplement for weight reduction. All patients developed acute hepatotoxicity and recovered spontaneously after withdrawal of dietary product. This product contains fenfluramine, n-nitroso-fenfluramine, and dried thyroid tissue powder. In Japan, the regulatory agency for drug and food safety received 120 reports of hepatotoxicity associated with Sennomotokounou between 2000 and 2002. Physicians should inquire about the use of dietary supplements whenever patients present with unexplained acute liver dysfunction.