Antioxidants are substances stable enough to prevent or delay the oxidation of easily oxidizable biomolecules such as lipids, proteins and DNA, thereby preventing oxidative damage (Lobo et al 2010). Antioxidants can be classified into two classes, according to their action, into primary antioxidants or chain breakers and secondary or preventive antioxidants. Primary antioxidants, when present in low concentrations, can delay or inhibit lipid oxidation by reacting with a lipid radical or peroxyl radicals. Secondary antioxidants, on the other hand, delay the rate of oxidation by chelating metal ions or quenching singlet oxygen (Amalia et al. 2005). These antioxidants are widely used as food additives in foods, especially those with high lipid content, to protect against oxidative degradation, maintain nutritional quality, and increase the shelf life of foods. In general, antioxidants can be divided into natural and synthetic antioxidants. Natural antioxidants are normally found in plant extracts which are believed to exhibit strong antioxidant activity and protection against oxidant-induced damage such as diabetes, neurodegenerative and cardiovascular diseases (Maganha et al. 2010). Plants, fruits, and vegetables are all known to be rich sources of natural antioxidants due to the presence of phenolic compounds, which are the secondary metabolites of plants (Misan 2010; Arya and Yadav 2011). Polyphenols, or phenolic compounds, constitute one of the most numerous and widely distributed groups of substances in the plant kingdom (Urquiaga and Leighton 2000; Gan et al. 2010). They exist naturally as glycosyls making them the most common water-soluble antioxidant compounds found in plants...... middle of paper ...... the antioxidant is effective at all stages (Jaswir et al 2004). A combination of antioxidants in which the antioxidants produce a synergistic effect can successfully inhibit lipid peroxidation. Recently, most studies have focused on the antioxidant activity of crude leaf extract and their individual polyphenols, only a few studies have investigated the interaction of crude leaf extract with other common antioxidants, including α-tocopherol. Furthermore, to date, there have been no scientific reports of an interaction between crude extract of young leaves of Aquilaria crassna and α-tocopherol. Therefore, in the present study, crude extract of agarwood (Aquilaria crassna) leaves is combined with α-tocopherol to investigate their antioxidant interaction against lipid peroxidation and to evaluate whether the interaction promotes a synergistic antioxidant effect..