Disclosed are: a novel modified protein A ligand having a superior property of causing the acid dissociation of antibodies compared to those of existing modified protein A ligands; and a novel modified protein A ligand having high alkali resistance. Specifically disclosed are: a protein having an affinity for an immunoglobulin, which is characterized by comprising an amino acid sequence produced by substituting at least one Gly residue by an amino acid residue other than an Ala residue in an amino acid sequence derived from any one of E-domain, D-domain, A-domain, B-domain and C-domain of protein A, and which is also characterized by having a reduced affinity for an Fab region contained in the immunoglobulin compared to a protein comprising an amino acid sequence produced by substituting the Gly residue by an Ala residue in the amino acid sequence derived from any one of E-domain, D-domain, A-domain, B-domain and C-domain of protein A; and a protein having an affinity for an immunoglobulin, which is characterized by having improved chemical stability under alkaline conditions compared to a corresponding domain.