DescriptionMetabolic syndrome (MetS) is a clustering of several cardiometabolic risk factors, including abdominal obesity, hyperglycemia, dyslipidemia and elevated blood pressure. More and more attention has been paid on MetS due to many reasons. For example, a quarter of the world’s adults have MetS, especially in developed countries; people with MetS has a five-fold greater risk of developing type II diabetes and three-times as likely to have a heart attack or stroke; and over 80% of the 200 million people with diabetes globally will die of cardiovascular diseases. In recent years, tea which is brewed from the plant Camellia sinensis has become increasingly popular for research because of its possible beneficial effects on human health, in particular in the area of MetS prevention. These beneficial qualities have mainly been attributed to catechins. In the present study, green tea polyphenols, Polyphenon E (PPE) and EGCG, were investigated in db/db and wild type mice to determine their effects on suppression of blood glucose level and activation of AMP-activated kinase (AMPK). Treatment of db/db mice with PPE (0.1% i.g.) or EGCG (200 or 400 mg/kg) decreased the level of blood glucose and increased the level of insulin both in blood or pancreas. Further, EGCG at 100, 200, and 400 mg/kg time- and dose-dependently up-regulated the phosphorylation of AMPK in liver, but it did not increase the oxidative stress. Melatonin, a strongly anti-oxidative compound, at 50 mg/kg (i.g.) was unable to block the effects of EGCG on activating AMPK. Together, these data suggest that green tea polyphenols or EGCG can alleviate MetS possibly through the activation of AMPK in liver, and the activation of AMPK by EGCG appears not to involve the reactive oxygen species in mice.