Introduction: The aim of the present study was to evaluate the preventive effects of Flavin7 in prediabetic bio-breeding diabetes prone (BB-DP) rats. Methods: Foutthy rats were divided into 2 equal groups: group C (untreated control group) and group F7 with Flavin7 (natural dietary supplement F7 with bioflavonoids, 0.2 mg/l) in drinking water from 21st day after birth to 171st day of their life, respectively. Blood glucose, superoxide dismutase, glutathione peroxidase, catalase, total antioxidant capacity, glutathione, body weight, food intake, water intake and urine output were determined.  Results: The age of diabetes onset was significantly higher for group F7 compared to group C (P<0.05). The incidence of diabetes was lower in group F7 than in group C. Blood glucose at the diabetes onset was higher in group C than in F7 group (P<0.05). Decrease of antioxidant status parameters, at the treatment onset as well as immediately after its termination showed a drop in the F7 group firstly, but increased progressively later, until the end of the experiment. Conclusion: F7 delayed the development of diabetes in BB-DP rats and prevented its onset. The severity of diabetes mellitus was milder in rats treated with F7 than in control group.