Peppermint plants have been used as a herbal medicine for many conditions, including loss of appetite, common cold, bronchitis, sinusitis, fever, nausea, vomiting and indigestion. This study is aimed at investigating the biochemical and histological effects of Mentha piperita L., growing in the Yenisar Bademli town of Isparta City, and Mentha spicata L., growing on the Anamas high plateau of Isparta City, on rat kidney tissue. Forty-eight male Wistar albino rats weighing 200-250 g were used for this study. Animals were divided into four experimental groups, each with 12 rats, as follows: control group (group I); 20 g/L M. piperita tea (group H); 20 g/L M. spicata tea (group III); 40 g/L M. spicata tea (group IV). The control group rats were given commercial drinking water (Hayat DANONESA water). The tea for the other groups was prepared daily and provided at all times to the rats during 30 days as drinking water. Plasma urea and creatinine levels were determined, and the levels of thiobarbituric acid reactive substance (TBARS) and the activities of glutathione peroxidase (GSH-Px), catalase (CAT) and superoxide dismutase (SOD) were studied in the homogenates of kidney tissue. The levels of plasma urea and creatinine were increased significantly (P < 0.0033) in groups III and IV when compared with group I. The activities of SOD and GSH-Px were decreased significantly (P < 0.0033) in group IV when compared with group I. The activities of CAT were decreased significantly in groups III and IV (P < 0.033, P < 0.0033, respectively) when compared with group L TBARS levels were increased significantly (P < 0.0033) in groups III and IV when compared with group I. In groups II, III and IV, hydropic degeneration of tubular epithelial cells, the epithelial cells with picnotic nuclei and eosinophilic cytoplasm, tubular dilatation and enlargements in Bowman capsules were observed histologically. However, in group H histopathological changes were more slight than in groups III and IV. In group IV, in addition to these changes, extremely hydropic degeneration of tubular epithelial cells, some atrophic tubules and glomerules, and focal mononuclear cell infiltrations in the kidney tissues of the rats were observed. In conclusion, the results indicate that M. piperita does not show nephrotoxicity but M. spicata presents markedly nephrotoxic changes in rats.