OBJECTIVE L-theanine is the unique amino acid found in tea plants, has antioxidant and antiinflammatory activities, and functions in mental concentration and sleep quality. In this study, it is aimed to investigate the effects of L-theanine on doxorubicin (DOX, a chemotherapeutic agent) induced nephrotoxicity in rats, especially via GSH related enzymes. METHODS 32 male Sprague Dawley rats weighing 300-400 g were randomly assigned into 4 groups (n = 8) and the substances were given intraperitoneally to them: Control group (saline for 5 days); Theanine group (200 mg/kg/day theanine for 5 days); DOX group (single dose of 20 mg/kg DOX); DOX + Theanine group (20 mg/kg DOX at first day and 200 mg/kg/day theanine for 5 days). Kidney tissues were evaluated by histopathological analysis. Serum levels of blood urea nitrogen (BUN) and creatinine by spectrophotometrically; percentage of apoptosis indexes (AI%) in the tissues by TUNEL method; caspase-3 levels, reduced and oxidized glutathione (GSH and GSSG), gamma-glutamyltransferase 1 (GGT1), glutathione reductase (GR), glutathione peroxidase (GPx), and glutathione S-transferase (GST), nuclear factor kappa B p65 (NF-kB p65) by commercial kits; malondialdehyde (MDA) by spectrophotometrically were determined in plasma and kidney tissues. RESULTS According to DOX group, the DOX + Theanine group has much lower tissue and plasma GSSG, GGT1, NF-κB p65 levels and tissue AI%, whereas significantly higher GSH levels and GPx, GR, GST activities (P < 0.05). CONCLUSIONS It is suggested that L-theanine may have protective effects by enhancing effects on the antioxidant system of GSH and GSH-related enzymes against DOX-induced nephrotoxicity in rats. But this finding needs to be supported with further studies.