Excessive amounts of reactive oxygen species (ROS), unless counterbalanced by antioxidants, can cause cellular damage under oxidative stress conditions; therefore, antioxidative defenses against ROS must be measured. With the development of nanotechnology, nanoparticles have found numerous applications in science, health, and industries. Magnetite nanoparticles (Fe3O4:MN Ps) have attracted attention because of their peroxidase-like activity. In this study, hydroxyl radicals (center dot OH) generated by MNPs-catalyzed degradation of H2O2 converted the N,N-dimethyl-p-phenylenediamine (DMPD) probe into its colored DMPD center dot+. radical cation, which gave an absorbance maximum at lambda = 553 nm. In the presence of antioxidants, center dot OH was partly scavenged by antioxidants and produced less DMPD center dot+, causing a decrease in the 553 nm-absorbance. Antioxidant concentrations were calculated with the aid of absorbance differences between the reference and sample solutions. The linear working ranges and trolox equivalent antioxidant capacity coefficients of different classes of antioxidants were determined by applying the developed method. In addition, binary and ternary mixtures of antioxidants were tested to observe the additivity of absorbances of mixture constituents. The method was applied to real samples such as orange juice and green tea. Student t-test, F tests, and the Spearman's rank correlation coefficient were used for statistical comparisons.