Thearubigin (TR) has a wide molecular weight distribution, and the structure and formation mechanism have not been elucidated. The ethyl acetate-soluble fraction of a black tea infusion were applied to Sephadex LH20 chromatography in this study, and further TR fractions were obtained and analyzed by HPLC. The results show TR to be a fraction consisting of two components. The content of antioxidants was also measured during the manufacturing process for a black tea, with 40% showing radical scavenging activity.The radical scavenging activity of the ethyl acetate-soluble fraction changed during a black tea manufacturing process and decreased to approximately 20%.