The problem to be solved is to provide a humanized anti-IL-6 receptor antibody MRA-containing formulation which is suitable for subcutaneous administration, wherein dimerization or deamidation is prevented during long-term storage. The present application is directed to a stable antibody-containing liquid formulation characterized by containing arginine and histidine buffer. A method of inhibiting deamidation or dimerization of such an antibody in a concentrated liquid formulation includes histidine buffer in the liquid formulation.