Mangiferin is a poliphenolic compound used in the traditional South American and Indian medicine as a panaceum with antibacterial, antitumor, antidiabetic, and antiviral activity. Its main source is the bark and leaves of Mango tree (Magnifera indica L.). Several studies indicate mangiferin antioxidant properties. The purpose of our experiments was to study the possible inhibitory effect of mangiferin on lipid peroxidation, as an expression of its antioxidative capacity. We used the TBA-lipid peroxidation model according to Ernster and Nordenbrand in plasma from rats treated and untreated with mangiferin in both in vivo and in vitro conditions. In the in vitro non-treated rat plasma the amount of peroxidated lipids was 1.114±0.132 µmol/l, the addition of mangiferin (50 µmol/l) diminished this value to 0.720 ±0.025 µmol/l, which is a significant 35% reduction in lipid peroxidation. In plasma from the mangiferintreated rats (300 mg/kg, i.p.), the concentration of reaction products was at the level of 0.352±0.044 µmol/l; being 68% lower than in the untreated rats. We conclude that mangiferin is able to powerfully decrease lipid peroxidation. That indicates that mangiferin’s broad bioactivity should also have to do with its antioxidant properties.