As antioxidants and potential beneficial agents in cell transplantation, natural chalcone-tannin hybrids can protect mesenchymal stem cells against ROS-mediated damage. In their antioxidant abilities, galloyl moiety, 4-OH, and 2'-OH present antioxidant indexes of 0.58:0.13:0.29. The galloyl moiety enhances antioxidant levels of chalcone-tannin hybrids. Their antioxidant mechanisms may include Fe2+-chelating and direct radical scavenging, which comprises at least one electron transfer (ET). The Fe2+-chelating and ET may mainly occur in the galloyl moiety, while 4-OH without H-bonding interference prefers to donate H atom.