The aim of this work was to investigate the effects of St. John's Wort (SJW) extract treatment on behavioral changes arising in streptozotocin (STZ)-diabetic rats. Plus-maze, activity cage, modified forced swimming, and active avoidance tests were performed for evaluating exploratory behaviors, spontaneous locomotor activities, depression levels, and learning parameters of animals, respectively. Obtained data exhibited a diabetes mellitus (DM)-induced increase in anxiety and depression levels, decrease in spontaneous locomotor activities, and impairment of learning parameters in rats even in the early stages of the disease. Daily insulin replacement (2 IU/kg/day) could not restore these impaired parameters completely, indicating the need of novel therapeutic approaches. SJW extract (125 and 250mg/kg) treatments for seven days provided significant improvement in all of the impaired parameters observed in this study, probably due to its antidiabetic and central nervous system (CNS)-related effects.