Amyloidosis is defined as the extracellular deposition of non-branching fibrils composed of a variety of serum-protein precursors. Secondary amyloidosis is associated with several chronic inflammatory conditions, such as rheumatologic or intestinal diseases, familial Mediterranean fever, or chronic infectious diseases, such as tuberculosis. Although the association of amyloidosis with inflammatory bowel disease is known, amyloidosis secondary to ulcerative colitis (UC) is rare. A 36-year-old male patient with a 15-year history of UC presented with nausea, vomiting, and abdominal pain. He had been treated with infliximab for 6 years. At the time of admission, he had been undergoing treatment with mesalazine and adalimumab since the preceding 5 months. Esophagogastroduodenoscopy showed mucosal erythema, edema, and erosions with geographic ulcers at the 2nd and 3rd portions of the duodenum. Duodenal amyloidosis was diagnosed using polarized light microscopy and Congo red stain. Monoclonal gammopathy was not detected in serum and urine tests, while the serum free light chain assay result was not specific. An increase in plasma cells in the bone marrow was not found. Secondary amyloidosis due to UC was suspected. The symptoms were resolved after glucocorticoid therapy.