PM021, which consists of two herbal components, Mori Folium and Aurantii Fructus, is routinely used to treat diabetes in Korea. In this study, the anti-diabetic effect of PM021 on an animal model of developing type 2 diabetes of Otsuka Long-Evans Tokushima Fatty (OLETF) rats was investigated. Eight weeks of age male OLETF rats were treated daily with PM021 or vehicle for five months. Specifically, changes in body weight, blood glucose, urine volume, food intake and oral glucose tolerance were measured in rats for five months. The rats in this study were divided into four groups: a Long-Evans Tokushima Otsuka (LETO) rat group, which is a genetic control group for OLETF, that received no treatment; a PM021 treatment group of LETO rats; OLETF rats that received no treatment; and OLETF rats that received PM021 treatment. The results showed that PM021 significantly prevented increases in body weight, blood glucose, and urine and food intake that resulted from the induction of obesity and diabetes. PM021 also improved glucose tolerance in OLETO rats. However, PM021 had no effect on LETO rats, a control group of OLETF rats. Taken together, these findings indicate that PM021 has distinct anti-diabetic effects without any adverse effects or toxicities. Copyright © 2011 Elsevier Ireland Ltd. All rights reserved.