The antioxidant activity of a novel synthetic selenadiazole derivative SPO against DPPH and ABTS free radicals was evaluated using spectrometric methods. The results show that the detection wavelength and stable time for DPPH system were 515 nm and 30 min respectively, while those for ABTS system were 734 nm and 6 min, respectively. SPO could effectively and rapidly inhibited the formation of ABTS and DPPH free radicals in a dose- and time-dependent manner, indicating the potent antioxidant activity of SPO under both hydrophilic and hydrophobic conditions. In the optimized systems, the IC50 values of SPO were 85.2 μmol·L-1 (DPPH assay) and 36.5 μmol·L-1 (ABTS assay), respectively, which were comparable with the standard antioxidant Trolox, and significantly better than the positive controls BHA and BHT. Taken together, our results suggest the potential applications of selenadiazole derivatives as antioxidative agents.