The antioxidant activities of polyphenol stilbenoids have been extensively studied using different assays and methodologies regarding the structure-activity or structure-property relationship related to the position and number of OHs, and the electron-donating ability of stilbenoids has been discussed. Further, experimental data demonstrate that if the OH is scavenged or replaced by the methoxy group, the molecule loses its activity, suggesting that the OH is a proton donor and substituent with an electronic inductive effect. Thus, ROS scavenging activity was evaluated using the bond dissociation energy and ionization potential of the OH representing the antioxidant property of the individual OHs and entire molecule of stilbenoids. Consequently, several ROS scavenging mechanisms exist for piceatannol and other phenolic antioxidants, such as superoxide-facilitated oxidation, single-electron transfer (SET), sequential proton-loss ET, hydrogen-atom transfer (HAT), and proton-coupled electron transfer (PCET). At present, the antioxidant mechanism involves ET and proton transfer (PT); thus, HAT involving PCET via hydrogen bonds (HBs) is a plausible ROS scavenging/antioxidant mechanism rather than SET.