Cornelian cherry (Cornus mas L.) was in the past frequently used in Slovak Republic; meanwhile fell into oblivion despite the fact that it is known as antidiabetic supplement. However, there is no research investigated its effect on animal model of Diabetes mellitus (DM) 2 type as it is Zucker diabetic fatty (ZDF) rats. Thus, the aim of this study was to determine the effect of C. mas fruit given orally on the development of DM symptoms in ZDF rats. In the experiment male ZDF rats (fa/fa) and their age-matched non-diabetic lean controls (fa/+) were used aged 12 weeks. Male ZDF rats were administered C. mas in two doses (500 and 1000 mg/kg body weight) using a gastric gavage for 10 weeks. One group of diabetic animals served as positive control and received only distilled water. We found significant decrease of glucose level after oral administration of C. mas in dose of 1000 mg/kg bw in pre-diabetic state of animals (until 7th week of the experiment) and significant restriction of water intake in both C. mas groups against the diabetic control. We presume that the higher dose of Cornelian cherry could be beneficial and helpful in prevention of diabetic symptoms when consumed regularly in young animals.