A human antibody º type light chain complex-containing composition includes a complex in which a human antibody º type light chain is bound to one or more kinds of metal ions selected from the group consisting of Group 10 elements, Group 11 elements, and Group 12 elements. The human antibody º type light chain is a dimer, cysteines at C terminals of two human antibody º type light chains are bound to each other via the metal ion, and 0.1 mol or more of the metal ion is bound per 1 mol of the human antibody º type light chain.
