A method for analyzing the EGCg concentration in human serum was developed by using high-performance liquid chromatography with electrochemical detection. EGCg was detected in human serum after the ingestion of 5 g of green tea powder (matsu-cha) dissolved in 200 ml of hot water. The concentration of EGCg in the serum reached the highest level about 2 h after ingesting the green tea, and then decreased.