Humanized anti-tac (HAT) binding peptide is a peptide that can specifically bind to the Fc region of HAT. HAT is a humanized monoclonal antibody against the low affinity p55 subunit of the interleukin IL-2 receptor. Humanized anti-tac (HAT) binding peptide can be used to develop affinity chromatography media to purify specific monoclonal antibodies.