Diabetes mellitus comprises a heterogeneous group of metabolic diseases characterized by chronic hyperglycemia and impaired metabolism of carbohydrates, lipids and proteins caused by defects in insulin secretion or function. It is said to be the sixth factor of mortality and its complications, if untreated, include: atherosclerosis, nephropathy, neuropathy, foot ulcers, disability and death. To treat diabetes either insulin is administrated or some chemicals that lower blood sugar levels are prescribed. However, due to their various complications, the use of medicinal herbs has been increasingly taken into consideration. In this study, the effects of Hypericum extract on blood parameters in diabetic rats-male Wistar rats-were studied. Methods : In this study, male rats (n =36) were randomly divided into six groups: control, 21 day treated control, 28 day treated control, diabetic, 21 day treated diabetic rats, and 28 day treated diabetic rats. To induce diabetes, streptozotocin was used intraperitoneally at a single dose of 60 mg per 1kg body weight. The treated groups were gavaged with the extract at a dose of 60 mg per kg body weight in a period of 3-4 weeks. After this period, blood serum parameters were measured and the data were analyzed using multivariate analyze of variance Results : The results showed that there is a significant difference between the six groups in parameters FBS, Total P, and Na in blood, and PU, FBSU, KU in urine. Conclusion : The administration of Hypericum extract in the experimental models of diabetes mellitus has improved the biochemical parameters in diabetic rats.