Older adults experiencing chronic homelessness (i.e., prolonged homelessness and a disabling condition) have low rates of advance care planning (ACP) despite high rates of morbidity and mortality. Rehousing of homeless-experienced individuals into permanent supportive housing (PSH) may present an opportunity to introduce ACP; but this is unknown. Therefore, we explored staff and resident perceptions of conducting ACP in PSH. We conducted semi-structured interviews with PSH staff (n=13) and tenants (PSH residents) (n=26) in San Francisco. We used the capability (C), opportunity (O), motivation (M), behavior (COM-B) framework within the Behavior Change Wheel model and the Theoretical Domains Framework (TDF) to inform interviews, categorize themes, and guide qualitative thematic analysis. The mean age of PSH residents was 67 (SD=6.1) years and 52% were women. Of staff, 69% were women. Important COM-B barriers included ACP complexity (C), complicated relationship dynamics (O), resource limitations (O), pessimism (M), variable staff confidence (M), and competing priorities (M). Facilitators included easy-to-use documents/videos, including the PREPARE for Your Care program (C), stability with housing (O), exposure to health crises (O), potential for strong relationships (O), and belief that ACP is impactful (M). Recommendations included adapting materials to the PSH setting, providing staff trainings/scripts, and using optional one-on-one or group sessions. We identified behavioral determinants related to ACP for formerly chronically homeless older adults in PSH. Future interventions should include using easy-to-use ACP materials and developing resources to educate PSH residents, train staff, and model ACP in groups or one-on-one sessions.