ABSTRACT Purpose: To evaluate the effects of the experimental subcutaneous Walker-256 tumor and L-glutamine supplementation, an antioxidant, on the glomerular morphology of rats. Methods: Twenty Wistar rats were distributed into four groups (n = 5): control (C); control treated with 2% L-glutamine (CG); rats with Walker-256 tumor (WT); and rats with Walker-256 tumor treated with 2% L-glutamine (WTG). Renal histological samples were submitted to periodic acid-Schiff and Masson’s Trichrome staining to analyze glomerular density, morphometry of glomerular components and glomerulosclerosis; and to immunohistochemistry for fibroblast growth factor-2 (FGF-2). Results: WT showed 50% reduction in body mass gain and cachexia index > 10%, while WTG demonstrated reduction in cachexia (p < 0.05). WT revealed reduction of glomerular density, increase in the glomerular tuft area, mesangial area, matrix in the glomerular tuft, decrease in the urinary space and synechia, and consequently higher glomerulosclerosis (p < 0.05). L-glutamine supplementation in the WTG improved glomerular density, and reduced glomerular tuft area, urinary space, mesangial area, and glomerulosclerosis compared to WT(p < 0.05). WT showed higher collagen area and FGF-2 expression compared to C (p < 0.05). WTG presented lower collagen fibers and FGF-2 expression compared to WT (p < 0.05). Conclusions: L-glutamine supplementation reduced cachexia and was beneficial for glomerular morphology of the rats, as well as it reduced kidney damage and improved the remaining glomeruli morphology.