Around one third of stroke survivors develop depression at any point of time following the stroke event. Post-stroke depression (PSD) is associated with negative care outcomes including poorer function, longer hospital stays, increased outpatient and inpatient clinic use, and higher mortality rate. In Hong Kong (HK), the prevalence of PSD within the hospital setting was 36%, and up to 68% in the community setting. However, PSD is seldom addressed in either settings in HK and elsewhere. Meta-analyses reported the effectiveness of Internet-based cognitive behavioural therapy (iCBT), particularly when guided by therapists (d = 0.63). Personalised and synchronous instant message-based intervention guided by therapists is an emerging form of psychological intervention. While such intervention showed medium to large effect (Hedges' g = 0.73) on negative psychological distress episodes including depression, no study has investigated its effect on PSD. The proposed study aims to 1) investigate the effect of therapist-guided brief iCBT delivery through instant messaging applications (e.g. WhatsApp and WeChat) to provide personalised and synchronous PSD support and 2) understand the experience of and compliance with the intervention. 160 community-dwelling stroke survivors with Patient Health Questionnaire-9 (PHQ-9) scores ranging from 5 to 19 indicating mild to moderate depressive symptoms will be recruited and then individually randomised into the Intervention group (n=80) or Control group (n=80). Intervention group will receive 1) instant message-delivered brief iCBT for 3 months at participants' chosen times and frequencies, and 2) therapist-led text or voice message-based PSD support to enhance the effects of iCBT through real-time counselling and practical advice. Control group will only receive messages on general mental health information and reminders to participate in follow-up surveys. The primary outcome is PHQ-9 score at 6 months. Secondary outcomes will include anxiety (GAD-7), perceived stress (PSS-4), loneliness (ULS-8), and quality of life (EQ-5D-5L) at 6 months. The study will strictly follow the CONSORT-EHEALTH checklist. Post-trial qualitative study will be conducted to understand the participants' experience of and compliance with the intervention (n≈20) respectively. This study will provide the first and practical evidence on the effectiveness of instant message-delivered brief iCBT intervention in addressing PSD in HK and beyond.