BackgroundAdvance care planning (ACP) is highly relevant for people with early-stage dementia to communicate their care preferences for serious illness conditions with their family caregivers before they become mentally incapacitated.MethodsA multi-centre, quasi-experimental study was conducted to test the feasibility and acceptability of a theory-guided, dyadic ACP intervention (‘Have a Say’ programme) among participants with early-stage dementia–family caregiver dyads. The feasibility of the trial design, intervention procedures, subject recruitment and retention, and study instruments were assessed. Study outcomes were measured at baseline (T0), immediately after the intervention (T1), and at 1 month (T2) and 3 months post-intervention (T3). Acceptability of the intervention was determined by the satisfaction score, completion rate and qualitative interviews as process evaluation with a purposive sample of participants and ACP facilitators. Generalised estimating equations were performed to examine differential changes between groups over time, with covariates adjusted.ResultsSubject recruitment from five elderly community centres yielded a recruitment rate of 60% and resulted in 36 client–caregiver dyads. The intervention was acceptable to the dyads, with a mean satisfaction score of 4.4 out of 5 and completion rate of 94.4%. The attrition rates at T1, T2, and T3 were 8.3%, 13.9%, and 19.4%, respectively. The intervention group reported a significantly greater improvement in the readiness for ACP at T1, self-efficacy for ACP at T3, and dyadic concordance on end-of-life care preferences at all time points than the control group, but not on depressive symptoms. Family caregivers in the intervention group reported a significantly higher caregiving burden at T2 than the control group. The qualitative findings revealed that triadic involvement of and trusting relationships among the dyads and ACP facilitators, and documentation of clients’ views are the programme strengths, while the structured format and discussion about medical issues posed implementation challenges.ConclusionsThis ACP intervention and trial design were feasible and acceptable to the dyads. Several refinements were identified, including adding a nurse-led group-based session for information giving, allowing flexibility in arrangement, and adding measure of ACP engagement of family caregivers. A rigorous trial to test the effects of the ACP intervention is warranted.Trial registrationRetrospectively registered on 14/08/2020 at clinicaltrials.gov (Identifier: NCT04513106).