Abstract: The prevalence of sleep disorder is high in patients with ulcerative colitis (UC), and the relationship between sleep disorder and UC is complex. The core mechanisms underlying the comorbidity of UC and sleep disorder primarily involve dysfunction of the gut–brain axis and disruption of the circadian rhythm, in which abnormal expression of clock genes, melatonin dysfunction, and gut microbiota dysregulation play unique roles. In terms of treatments, psychological and behavioral interventions, nutritional supplementation, and lifestyle adjustment could contribute to improve sleep, besides therapies aimed at controlling the primary disease. Future researches should strengthen the investigation of the causal mechanisms between the two and establish more standardized intervention measures, integrating sleep management into the comprehensive diagnosis and treatment for UC.