Objective Patients with ANCA-associated vasculitis (AAV) experience high levels of fatigue, despite disease remission. This study assessed the feasibility and acceptability of a definitive randomized controlled trial of a behavioural-based physical activity intervention to support fatigue self-management in AAV patients. Methods AAV patients in disease remission with fatigue (Multidimensional Fatigue Inventory-20 general fatigue domain ≥ 14 ) were randomly allocated to intervention or standard care in this single-centre open-label randomized controlled feasibility study. The intervention lasted 12 weeks and comprised eight face-to-face physical activity sessions with a facilitator and 12 weekly telephone calls. Participants were encouraged to monitor their physical activity using a tracker device (Fitbit). Standard care involved sign-posting to fatigue websites. The primary outcome was feasibility of a phase III trial assessed against three stop/go traffic light criteria, (recruitment, intervention adherence and study withdrawal). A qualitative study assessed participant views about the intervention. Results A total of 248 patients were screened and 134 were eligible to participate (54%). Stop/go criteria were amber for recruitment; 43/134 (32%, 95% CI: 24, 40) eligible participants randomized, amber for adherence; 73% of participants attended all eight physical activity sessions, but only 11/22 (50%, 95% CI: 29, 71%) completed the intervention as per the intended schedule, and green for study withdrawal; 2/43 participants withdrew before 24 weeks (5%, 95% CI: 0, 11). Qualitative results suggested the intervention was acceptable. Conclusion This study suggests a behavioural-based physical activity intervention targeting fatigue self-management was acceptable to patients with AAV, although recruitment and protocol adherence will need modification prior to a definitive trial. Clinical Trial Registration Number ISRCTN11929227. [ABSTRACT FROM AUTHOR]