In previous studies, we found the production of antibodies against cross-reactive bovine serum albumin (BSA) in D-galactose (D-gal) induced aging mouse models. We performed immunoblot analysis with mouse tissue lysates to investigate the changes in the overall autoantibody production in this animal model. And we were able to see the possibility of altering the activity of mouse natural antibodies in this process. In this study, we examined changes in existing natural antibodies in a D-gal-induced aging mouse model. Serum samples were collected from 3-week-old mice (3w), 13-week-old mice (13w), and 13-week-old mice that were treated with D-gal for 6 weeks (13wDG), beginning at the age of 8 weeks. Levels of immunoglobulins (IgM, IgG, and IgA) were quantitatively analyzed in serum samples. Tissue samples were obtained from skin, spleen, and ovary for Western blotting analyses. Natural antibody activity was examined by enzyme-linked immunosorbent assay analyses of anti- double-stranded DNA (dsDNA) antibody. Western blotting analyses using mouse tissue lysates showed that several protein bands detected by serum antibodies from 3w mice became increasingly thicker when detection was performed with serum samples from 13w and 13wDG mice, indicating quantitative increases in levels of natural antibodies. Relative amounts of total IgG, IgM, and IgA immunoglobulins sequentially increased in serum samples from 3w, 13w, and 13wDG mice. A similar tendency was observed regarding the levels of IgM and IgG antibodies against dsDNA. These results indicate increased levels of natural antibodies in the D-gal-induced aging mouse model. Therefore, this animal model could be useful for future natural antibody research.