Autoantibodies against DNA are IgG type or IgM type reacting with natural double stranded DNA (dsDNA), single-stranded DNA (ssDNA), or both types. In human SLE (systemic lupus erythematosus), there found anti-dsDNA-IgG with high incidence. In SLE blood anti-dsDNA titer closely related to DNA-anti-DNA complex and low complement level, and serves as an important marker for the activity of the disease. Experimental model animals with natural incidence of autoimmune diseases similar to those in human , and animals artificially induced inflammation have been used for elucidation of the mechanism of autoimmune diseases and also in searching for new drugs. A representative model animal of spontaneous autoimmune diseases is MRL/lpr mouse. As MRL/lpr shows high incidence of lymph node tumor, nephritis, angitis, and arthritis, this animal strain is useful for studies on incidence mechanism of human autoimmune diseases including rheumatoid arthritis. Autoantibodies found in MRL/lpr serum are IgG type rheumatoid factor, IgM type rheumatoid factor, anti-ssDNA antibodies, anti-dsDNA antibodies, and anti-Sm antibody, etc. This kit enables quantification and comparison of IgG type anti-ssDNA autoantibody with a calibration curve using standard antibody preparation.