Background and Objective: Hypericum perforatum is a plant which blooms between July and September at farms, borders of roads and woods, top of hills and grasslands, whose anti-inflammatory effects are shown in various studies. Due to this reason, a study is planned to examine the protective effects of Hypericum perforatumon nephrotoxicity caused by gentamicin. Materials and Methods:Gentamicin is administered to mice for 9 days to form nephrotoxicity and Hypericum perforatum extract is administered to mice for 9 days to evaluate protective effects. Cyclooxygenase-2, phospholipase A2 and inducible nitric oxide synthase enzymes in their kidneys are analysed by using ELISA method to compare the nephrotoxicity levels. Results: Gentamicin administration increased the expression of cyclooxygenase-2, phospholipase A2 and inducible nitric oxide synthase enzymes. Hypericum perforatum extract administration to mice that are administered gentamicin previously decreased the rate of increase of the cyclooxygenase-2 and inducible nitric oxide synthase caused by gentamicin while, it didn't have any effect on phospholipase A2 increase. Conclusion: Gentamicin caused an increase in cyclooxygenase-2, phospholipase A2, inducible nitric oxide synthase enzymes in kidneys. Application of Hypericum perforatum extract decreased the increase of cyclooxygenase-2 and nitric oxide synthase enzymes significantly while having no effect on the increase of phospholipase A2. In conclusion, this study shows that the gentamicin administration causes nephrotoxicity and the use of Hypericum perforatum extract can be helpful against this toxic effect.