The ameliorative effect of DL-tryptophan on dextran sulphate sodium (DSS)-induced ulcerative colitis (UC) in mice was investigated. The alcohol extract of quinoa was obtained using the ultrasonic-assisted extraction method, followed by isolation and purification. DL-tryptophan was identified as the primary component through compositional analysis. The anti-inflammatory effect of quinoa DL-tryptophan was assessed using RAW264.7 macrophage cells to establish an inflammation model. Wild-type C57BL/6 mice were used as study subjects and were administered 50 mg/kg of pure DL-tryptophan daily through oral gavage; the anti-inflammatory effect of quinoa DL-tryptophan was then evaluated using the DSS-induced UC model. The ameliorative effects of DL-tryptophan were assessed by monitoring changes in body weight and surface characteristics, assessing Disease Active Index (DAI) scores, measuring colon length, and performing hematoxylin and eosin staining and immunofluorescence staining. The expression of tumor necrosis factor (TNF-α) and interleukin 1β (IL-1β) in the colon tissues of the mice were detected using enzyme-linked immunosorbent assay to assess the ameliorative effect of DL-tryptophan on DSS-induced UC mice. Compared with the model group, the DAI score in the DL-tryptophan group decreased by 50.64%, whereas the average body weight and colon length increased by 5.03 g and 2.23 cm, respectively. In addition, the DL-tryptophan group showed decreased number of intestinal cup cells and improved mucosal damage, and the expression levels of TNF-α, IL-1β and other inflammatory factors in the colon tissue significantly decreased (P<0.01). The expression of tight junction proteins claudin-1, occludin, and ZO-1 in intestinal epithelial cells was recovered. In summary, DL-tryptophan ameliorates DSS-induced UC in mice by decreasing the secretion of inflammatory factors and restoring the expression of tight junction proteins, thereby alleviating intestinal inflammatory responses.