Background: Device-measured daily steps/step cadence and other prominent behaviours occurring throughout the 24-hour day (i.e., sitting, lying, standing) have not been examined in patients with ulcerative colitis (UC). The degree to which these behaviours are associated with mental health, quality of life and clinical outcomes in this population is unknown. Aims: To explore the associations between device-based walking, step cadence, and sedentary time and clinical outcomes among UC patients. Methods: Patients with UC wore an activPAL TM accelerometer for 7 days to measure daily steps, step cadence, lying, standing, and sitting time. Outcomes included total Mayo score (TMS), risk of depression (PHQ-8), risk of anxiety (GAD-7), and health-related quality of life [HRQoL (SF-12)] which included mental composite scores (MCS) and physical composite scores (PCS). Blood and stool samples were used to measure C-reactive protein (CRP) and fecal calprotectin (FCP). Results: Of 30 participants, thirteen (43.3%) had moderate to severe UC symptoms. The percentage of patients with moderate to severe depression and anxiety symptoms were 25.0% and 57.1%, respectively. Average daily steps were 7,869 3339. Step cadence ≥ 100 steps/min was positively associated with mental HRQoL and TMS, and inversely associated with FCP. Standing time was positively associated with TMS and inversely associated with depression, anxiety, and FCP. Faster walking was negatively correlated with CRP. Conclusion: This study identifies potential associations between device-measured brisk walking/running and periods of standing with HRQoL, mental health, and clinical outcomes. This study should be replicated in a larger sample to determine if these associations remain.