Trace amounts of colored impurities, which remained in recombinant human serum albumin (rHSA) after purification by several steps of chromatography, were removed by immunoadsorption. The impurities were collected as a pass-fraction through an affinity column coupled with anti-HSA antibody raised against HSA from human serum and were used for immunization to obtain antibodies against the impurities. By immuno-adsorption with the antibodies thus obtained, the colored impurities in rHSA were effectively removed.