Nine male volunteers were given 36 g of cocoa powder (containing 2610 mg of polyphenols) per day with sugar and 6 volunteers received an equivalent amount of sugar for 2 weeks. Conjugated diene production in LDL induced by 2-2' azobis(4-methoxy-2,4-dimethylvaleronitrile) (V-70) and copper ion were evaluated. The lag time was significantly prolonged at 1 and 2 weeks in V-70 and at 2 weeks in copper ion after cocoa powder consumption. The level of excretion of epicatechin in urine was significantly higher in the cocoa group than that in the control group. In conclusion, the antioxidants in cocoa powder might be absorbed and increase the resistance of human LDL to oxidation.