In this study, we examined the beneficial effects of Chlorella, Spirulina, and astaxanthin on methotrexate-induced oxidative injury in the kidney and liver. Astaxanthin, spirulina, and chlorella were administered orally to male mice for 8 days, and on the 5th day, methotrexate was intraperitoneally injected into the mice. The results revealed that methotrexate caused a significant decrease in body weight and food and water intake, along with a significant increase in serum AST, ALT, urea, and creatinine levels compared with controls. Methotrexate-induced oxidative effects were revealed by a marked decrease in catalase and glutathione S-transferase (GST) activity. Chlorella, Spirulina extracts, and astaxanthin markedly reversed the above-altered parameters, suggesting, therefore, their potential use for alleviating the harmful effects of methotrexate in mice. The observed biochemical changes in the treated animals compared with those of controls were supported by the liver and kidney histopathological changes.