Chronic inflammatory disease such as Ulcerative Colitis (UC) and Crohn’s Disease (CD) causes excessive fibrosis and strictures in the intestine. An intestinal fibrosis model using dextran sodium sulfate (DSS)-induced UC in mice was investigated to determine new treatment methods for UC. DSS containing drinking water was given to C57BL/6N mice for 7 days, followed by 14 days of water (repeated three times). Animal body weight, blood in the feces, fecal consistency, and disease activity index (DAI) were evaluated. To evaluate inflammation, myeloperoxidase (MPO) activity was determined and hematoxylin and eosin (H&E) staining was performed. Masson's trichrome, Picrosirius red staining, immunohistochemistry (IHC) and western blotting were used to evaluate the degree of fibrosis. The DSS group had higher DAI scores, a reduction in goblet cells, infiltration of lymphocytes, and higher MPO activity than the control group. Increased collagen fiber deposition in the colon and increased type I collagen in the lamina propria and submucosal tissue was evident in the DSS group, with myofibroblasts in the lamina propria. Heat shock protein-47 and tissue inhibitor of metalloproteinases-1 were detected. Repeated DSS intake exacerbates colitis with lymphocyte infiltration and fibrosis, with an increase in type I collagen in the lamina propria and submucosal tissue.