IntroductionSELF-BREATHE is a complex, transdiagnostic, supportive, digital breathlessness intervention co-developed with patients. SELF-BREATHE seeks to build capacity and resilience within health services by improving the lives of people with chronic breathlessness using nonpharmacological, self-management approaches. This study aimed to determine whether SELF-BREATHE is feasible to deliver and acceptable to patients living with chronic breathlessness.MethodsDesign: A parallel, two arm, single blind, single centre, randomised controlled mixed-methods feasibility trial with participants allocated to 1) intervention group (SELF-BREATHE) or 2) control group (usual NHS care).SettingLarge multisite NHS Foundation Trust in Southeast London.ParticipantsPatients living with chronic breathlessness due to advanced malignant or non-malignant disease(s).InterventionParticipants were randomly allocated (1:1) to an online, self-guided, breathlessness, supportive intervention (SELF-BREATHE) and usual care or usual care alone, over six weeks.A priori progression criteria≥30% of eligible patients given an information sheet consented to participate,≥60% of participants logged on and accessed SELF–BREATHE within 2 weeks, ≥70% of patients reported the methodology and intervention as acceptable.ResultsBetween January 2021 and January 2022, 52/110 (47%) eligible patients consented and were randomised. Of those randomised to SELF-BREATHE, 19/26 (73%) logged on and used SELF-BREATHE for a mean (sd, range) of 9 (8, 1–33) times over 6-weeks. Thirty-six of the 52 (70%) randomised participants completed and returned the end of study postal questionnaires. SELF-BREATHE users reported it to be acceptable. Post intervention qualitative interviews demonstrated that SELF-BREATHE was acceptable and valued, by users, improving breathlessness during daily life and at points of breathlessness crisis.ConclusionThese data support the feasibility of moving to a fully powered, efficacy, randomised controlled trial with minor modifications to minimise missing data (i.e., multiple methods for data collection, face-to-face, telephone, video assessment andviapost).