Chalcones are the starting materials for the biosynthesis of flavonoids. Flavonoids are strong antioxidants, which contain many phenolic hydroxyl group(s). However, the antioxidant activities of chalcones have been little studied. In this study, chalcones with chemical structures resembling natural chalcones were synthesized, and the effects of the hydroxyl group(s) on the A and B rings and the C3 chain connecting the A and B rings were investigated in detail. Hydroxyl group(s) on the B ring inherited the characteristics of p-coumaric acid as a precursor of chalcone, if the groups were located on 2- and/or 4-positions to the C3 chain, and showed strong antioxidant activities. The 2'-hydroxy group of the A ring cooperated with the carbonyl group on the 1'-position to provide ultraviolet rays absorbing (photo-antioxidant) activity. The carbon-carbon double bond in the C3 chain, connecting the A ring with the B ring in a conjugated system, enhanced both anti?oxidant and photo-antioxidant activities. The obtained information was used in the molecular design of new polymer additives.