We investigated the effects of Polygonum tinctorium Lour (PTL), a plant commonly known as indigo, on biological parameters in an animal model of high-fat diet-induced obesity. Wistar rats fed a high-fat diet and treated with PTL showed lower serum levels of triglycerides and total cholesterol levels and a higher serum levels of HDL cholesterol than those in Wistar rats fed a high-fat diet without PTL treatment. The weight of mesenteric fat in PTL-treated rats was decreased compared to that in control rats not treated with PTL. In addition, energy metabolic rate in the dark period, but not in the light period, in PTL-treated rats was higher than that in control rats. Although a significant difference was not observed, body weight in PTL-treated rats tended to be decreased compared to that in control rats. The results show that PTL improves serum lipid profiles in Wistar rats with high-fat diet-induced obesity. J. Med. Invest. 67 : 158-162, February, 2020.