An experimental study was carried out to evaluate the effect of Captopril on Gentamicin induced nephrotoxicity in rats in the Department of Pharmacology, Mymensingh Medical College and Dhaka Medical College, Bangladesh. Gentamicin antibiotic is most commonly employed clinically because of their potent bactericidal activities against Gram negative bacterial infections, less bacterial resistance, post-antibiotic effects and low cost. Gentamicin is associated with an induction of slow rises in serum creatinine, inflammation and perivascular edema, tubular degeneration and necrosis, tubular debris collection, glomerular atrophy which ultimately show the way to renal dysfunction. In spite of continued attractive efforts during the last decade, antioxidants like medicinal plants and different classes of drugs which were promised to reduce or ameliorate Gentamicin induced nephrotoxicity is yet a matter of debate. This study was aimed at inducing nephrotoxicity by injection Gentamicin and estimating the renal damage biochemically by measuring serum creatinine and perform histopathology of renal cortex in support of biochemical findings both in control groups, nephrotoxic and Captopril treated rats; also to determine the comparison between the concomitant and post effects of Captopril on control and nephrotoxic rats and to estimate the effect of Gentamicin withdrawal, 7 days after last injection in rats.