In this study, DEX downregulated the relative gene expression and protein expression of NFκB p65 and reduced the levels of proinflammatory cytokines, such as TNF-α and IL-1β, thus contributing to explain the reduction of ulceration and inflammation in the jugal mucosa of animals subjected to 5-FU-induced oral mucositis, as observed by the macroscopic and histopathological analysis. The gene discussed is IL1B; the disease is oral mucositis.