The inventors of the present invention found that by using a protein A column to purify a low pI antibody, performing an acid treatment and a neutralisation treatment, and thereafter, when a fixed time period has elapsed, performing a step for eliminating antibody aggregates that have been produced, subsequent antibody aggregation can be suppressed. Furthermore, the inventors found that by purifying a low pI antibody in the bind/elute mode of an anion exchange resin and further using a hydrophobic interaction chromatography or multimodal chromatography resin, it is possible to eliminate impurities more efficiently than conventional methods.
