Fu monisin B (FB) is a mycotoxin commonly found in maize and maize-based products. Ingestion of FB-contaminated causes a myriad of dose- and species-dependent toxic effects to human and animal health. In the present study we evaluated the effects of FB (8 mg/kg, i.p. for 4 days) on body weight and oxidative stress parameters in the liver, kidney and lung of C57BL/6 male mice. No changes in the organ-to-body weight ratio, organ-to-adrenal gland weight ratio or organ-to-brain weight ratio were found. On the other hand, FB exposure increased NPSH levels in liver and lungs whereas decreased FRAP content in liver and kidneys. Levels of TBARS, ascorbic acid and NOx content were not altered by FB. In summary, four days of FB exposure are sufficient to disrupt antioxidant defenses in liver, kidneys and lungs of C57BL/6 male mice without concomitant changes in organs weight.