Protein purification method

The present invention provides a simpler and less expensive method for purifying physiologically active proteins, especially antibodies, which can ensure removal of impurities such as DNA contaminants and viruses, and which can minimize a loss of physiologically active proteins. Means for Solving the Problems: A method for removing impurities in a physiologically active protein-containing sample, which comprises the following steps: 1) allowing the physiologically active protein-containing sample to be converted into an aqueous solution of low conductivity at a pH below the isoelectric point of the physiologically active protein; and 2) removing the resulting particles.