Th17 cells are critical members in mediating immune responses of adaptive immunity. In humans and mice, gut is a main site where Th17 cells are resided, and Th17 cell polarization also occurs in the gut. This process can be mediated by many factors, such as commensal bacteria, dendritic cells and cytokines, such as TGF-β and IL-6. Physiologically, polarized Th17 cells function in anti-infection and maintaining the integrity of intestinal epithelium. However, Th17 cells are plastic. For example, they will become pro-inflammatory cells if being exposed to IL-23. The pathogenic roles of Th17 cells have been well documented in inflammatory bowel disease. Besides, Th17 cells can accumulate in irradiated gut as well. Critically, radiation enteritis and inflammatory bowel disease present several similarities in disease pathology and pathophysiology. Herein, bacterial dysbiosis highly correlates with the pathogenicity of Th17 cells in inflammatory bowel disease. To our knowledge, radiation serves as a factor in inducing bacterial dysbiosis. Using this action, can Th17 cells be incited to promote inflammation in irradiated gut? In this review, we will sequentially introduce polarization of Th17 cells at steady state, radiation-induced Th17 accumulation in the gut, and advances in the management of radiation enteritis by using pharmacological therapy for bacterial dysbiosis.