Colistin, a glycopeptide antibiotic, is only used as an emergency treatment in case of multidrug-resistant bacterial infections. Due to its propensity for causing nephrotoxicity, colistin has a limited range of applications. In this study, the effect of colistin administration on kidney functions and oxidant/antioxidant status were investigated in rats. Twenty-four male rats were divided randomly into three equal groups. Control group; Colistin 7 group: received 300,000 IU colistin intraperitoneally twice daily for 7 days; Colistin 14 group: received 300,000 IU colistin twice daily for 14 days. The obtained results demonstrated a significant increase in serum urea, creatinine, uric acid, and renal Malondialdehyde (MDA) concentrations with marked decrease in serum albumin, renal glutathione (GSH) concentrations, and superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities in both colistin-administered groups when compared to the control. Additionally, colistin administered for 14 days exhibited significant alterations in the biochemical parameters compared to colistin 7 days administered rats group. In conclusion, colistin alters the renal oxidant/antioxidant status and elevates kidney function tests that are deteriorated by a long treatment period.