Abstract. This study aimed to investigate the possible protective role of curcumin against renal damage caused by administration of cyclosporine A (CsA) in adult male rats. For this purpose, 27 adult male albino rats were used and divided into three equal groups. Group I (control group) and group II (CsA-treated group) received a daily subcutaneous injection of CsA at a dose of 20 mg/kg b.w. Group III (prophylactic group) received a daily oral curcumin at a dose of 15 mg/kg b.w. simultaneously with CsA. After 21 days, all the animals were anaesthetized and the kidneys were rapidly removed and processed to prepare paraffin sections stained with H&E, PAS and Masson's trichrome. In addition, the glutathione S-transferase (GST) enzyme was detected immunohistochemically. The optical density and the area (in %) of positive GST immunoreactions were measured in the cytoplasm of renal tubules and glomeruli and the data were statistically analyzed. Examination of sections from CsA-treated group showed renal tubules with vacuolated cytoplasm and others with darkly stained pyknotic nuclei. Apical brush borders of proximal tubules were undefined and PAS positive granules were noticed in their cytoplasm. The renal corpuscles contained shrunken glomeruli with widening of their Bowman's spaces. Inflammatory cellular infiltrate and increase in the collagen fibers were observed between the renal tubules. In prophylactic group, the structure of renal tubules and corpuscles were preserved except few tubular darkly stained pyknotic nuclei. Numerous blood vessels, few cellular infiltration and thin collagen fibers were observed between the renal tubules. Statistical analysis of morphometric data showed significant increase in the optical density of GST immunoreactivity in the cells of renal tubules and glomeruli of CsAtreated group when compared with the control or prophylactic groups. However, a significant decrease in the area of GST immunoreactivity in sections from prophylactic group was observed when compared with control or CsA-treated groups. In conclusion, protective effect of curcumin against cyclosporine-induced nephrotoxicity in rats was proven based on the study of histological changes and GST immunoexpression. This study supposes the possible therapeutic applications of curcumin in CsA-treated patients.