Aim: To explore barriers, facilitators and preferences for engagement in a co-designed package of five social prescribing activities addressing social frailty among older informal carers to inform intervention enhancements before implementation. Methods: Semi-structured interviews were conducted with 13 informal carers aged ≥55 years in NSW either online or over the phone between November-December 2025. Participants were experiencing loneliness and/or social frailty as assessed by the UCLA-4 and SFS-8. Interviews explored carer’s willingness to engage in a range of social, physical and wellbeing-focused activities, alongside perceived barriers, facilitators, and preference rankings using an adapted Nominal Group Technique. Data were analysed thematically. Results: Low-burden wellbeing activity (i.e. meditation) that could be attended online was ranked highest overall, followed by gentle strength with balance exercise, and reminiscence. Less popular were senior internet skills and problem-solving book club. Participation in the proposed activities was shaped by caregiving demands, time constraints, accessibility, and alignment with personal preferences. The inability for carer to leave the care recipient and lack of respite were the significant barriers to participation. Additional envisaged barriers included competing commitments and transport limitations, particularly for participants outside of major cities. Facilitators for engagement included perceived opportunities for social connection, anticipated health benefits, and flexible delivery options such as online or local sessions. Conclusions: Carers favoured options that could be accessed virtually or locally and required minimal time commitment. The findings suggest that enhancing flexibility and access to respite support may be critical to optimising participation and addressing social frailty among older informal carers.