Background and Aim: Diabetes mellitus (especially type I) is accompanied with disturbances in learning, memory, and cognitive skills in the human beings and experimental animals. Considering the potential nootropic effect of the medicinal plant Hypericum perforatum (HP), therefore, this study was conducted to evaluate the effect of long term oral administration of HP aerial part on learning and memory in diabetic rats by use of passive avoidance test.Materials and Methods: In this study, male Wistar diabetic rats were randomly divided into control, HP-treated control, diabetic, and HP-treated diabetic groups. HP treatment continued for 1 to 2 months. For induction of diabetes a single dose of streptozotocin 60mg/kg was injected i.p. Serum glucose level-was determined before the study and at the 4th and 8th weeks after the experiment. In addition, for evaluation of learning and memory, initial latency (IL) and step-through latency (STL) were determined after 1 and 2 months using passive avoidance test.Results: One- and two-month administration of HP aerial part at a weight ratio of 1/15 did not show any significant hypoglycemic effect in treated control and diabetic groups. Furthermore, there was a significant increase (p<0.05) in IL in diabetic and HP-treated diabetic groups after two months as compared to control group. In this respect, there was no significant difference between diabetic and HP-treated diabetic groups. In addition, STL significantly increased in HP-treated control group after 1 (p<0.05) and 2 (p<0.05) months in comparison with control group. on the other hand, STL significantly decreased (p<0.05) in diabetic group and significantly increased (p<0.05) in HP-treated diabetic group as compared to control group after two months.Conclusion: In summary, long term oral administration of HP aerial part could enhance the recall capability of stored information in control and diabetic animals.