The effect of heat-treated Chinese quince polyphenols on plasma antioxidant activity and the plasma levels of aromatic acids after oral administration to rats was investigated. The aqueous solution of Chinese quince polyphenols (CP) that had been extracted using 60%(v/v) acetone turned reddish during the heat treatment in the presence of citric acid. During the treatment, decreases in polymeric procyanidins and an increase in monomers, dimers and oligomers were observed. In the oral administration study, CP subjected to 2 h of heat treatment (CPT-2) caused a significant increase in antioxidant activity as assessed by the ferric reducing ability of plasma (FRAP) method. In addition, CP, CP + citric acid and CP subjected to 8 h of heat treatment (CPT-8) also tended to increase the FRAP value but the increase was not significant. Of the plasma aromatic acids detected, protocatechuic acid increased in all rats given the polyphenols. Vanillic acid increased significantly in rats given CPT-2 and CPT-8, reflecting a facilitatory effect of heat treatment on the intestinal absorption of protocatechuic acid and subsequent conversion by catechol-O-methyl transferase.These results suggested that the heat-induced breakdown of Chinese quince polyphenols seems to be an effective method of leading to an elevation of plasma antioxidant activity and levels of aromatic acid that are health-benefiting compounds derived from procyanidins.