The pathogenic relationship of ulcerative colitis and rheumatoid arthritis is not known. Therefore, we examined dextran sodium sulfate (DSS)-induced colitis separately and in combination with a mouse arthritis model that mimics rheumatoid arthritis and evaluated the deterioration-related factors of each condition. Arthritis was induced in a collagen-induced arthritis mouse model using DBA/1JJmsSlc mice and ulcerative colitis was induced by the administration of drinking water containing 3.0% (w/v) DSS. The arthritis/DSS-treated mice developed worse colitis scores compared to that of the other groups of mice. The arthritis/DSS-treated mice did not demonstrate changes in hind foot volumes or in the concentration of matrix metalloproteinase-3 (MMP-3) in the plasma; however, plasma levels of interleukin-6 (IL-6) and tumor necrosis factor (TNF)-α were increased. Our results showed that IL-6 and TNF-α may influence the deterioration effect of colitis in arthritic mice.