Background and Aim Gentamicin antibiotic has some side effects such as nephrotoxicity. The aim of this study was to evaluate the post-treatment effects of using hydroethanolic extract of Origanum vulgare (Ov) on neph� rotoxicity caused by gentamicin.Methods & Materials In this study, 32 male Wistar rats were divided into four groups of control (n=8), gentami� cin (n=8; 100 mg/kg/day intraperitoneally for 8 days and gavage of distilled water for 2 days), Ov extract group (intraperitoneal injection of normal saline for 8 days and using 40 mg/kg Ov extract by gavage for 2 days), and gentamicin+ Ov extract (intraperitoneal injection of gentamicin 100 mg/kg/day for 8 days and using 40 mg/kg Ov extract by gavage for 2 days). The concentration of urea, creatinine, sodium, potassium and osmolarity were measured in plasma and urine samples. The right kidney was used to measure Malondialdehyde (MDA) and Ferric Reducing Antioxidant Power (FRAP). Ethical Considerations This article was obtained from a research proposal approved by the Research Ethics Com� mittee of Arak University of Medical Sciences (Code:IR.ARAKMU.REC. 1394.284) Results Post-treatment administration of hydroethanolic extract of Ov significantly decreased the concentration of urea, creatinine, absolute sodium excretion, relative sodium and potassium excretion, and MDA levels but significantly increased creatinine, urine osmolality and FRAP levels. Conclusion Oral administration of Ov extract as post-treatment method improved nephrotoxicity caused by gen� tamicin use by reducing oxidative stress of oxygen free radicals and lipid peroxidation in the affected kidneys.