Objective:To investigate the association of malnutrition based on Global Leadership Initiative on Malnutrition (GLIM) criteria with the disease activity and clinical outcomes in hospitalized ulcerative colitis (UC) patients.Methods:Clinical data of 115 patients with UC hospitalized in the Affiliated Hospital of Qingdao University from September 2019 to March 2023 were prospectively analyzed. GLIM and European Society for Clinical Nutrition and Metabolism (ESPEN) 2015 criteria were used for the diagnosis of malnutrition, allowing the analysis of consistency between two diagnostic criteria for malnutrition. The relationship between malnutrition based on GLIM criteria and disease activity and clinical outcome was further investigated. The risk factors of adverse clinical outcomes in UC patients were analyzed using binary logistic regression.Results:GLIM and ESPEN 2015 diagnostic criteria showed high correlation and consistency (AUC=0.875, P<0.001; K=0.809, P<0.001). According to GLIM criteria, the prevalence of malnutrition among hospitalized UC patients was 32.17% (37 cases). Compared with non-malnourished UC patients, the modified Mayo score and C-reactive protein level of malnutrition patients were higher ( P<0.005), and the proportion of patients with severe disease activity was higher ( P=0.005). UC patients in the malnourished group had longer hospital stay ( P<0.001), higher hospitalization costs ( P<0.001), and higher rates of drug escalation/conversion therapy, re-admission and surgery at 12 weeks and 54 weeks ( P<0.05). Binary logistic regression analysis showed that a high Mayo score ( OR=3.606, P=0.016), a high modified Mayo score ( OR=1.346, P=0.009) and malnutrition ( OR=1.430, P=0.012) were independent risk factors for adverse clinical outcomes of hospitalized UC patients at 12 weeks. A high modified Mayo score ( OR=6.491, P=0.011) and malnutrition as per GLIM criteria ( OR=6.693, P=0.033) were independent risk factors for adverse clinical outcomes of hospitalized UC patients at 54 weeks. Conclusions:GLIM and ESPEN 2015 diagnostic criteria show high consistency in the diagnosis of malnutrition in hospitalized UC inpatients. Malnutrition may imply adverse clinical outcomes of hospitalized UC patients, which is an independent risk factor for the adverse clinical outcome of hospitalized UC patients.