Purpose: Perioperative physical activity behavior change in older adults with cancer is complex. Identifying the barriers and facilitators to physical activity before and after surgery can help predict adherence and optimize outcomes. We aimed to determine the barriers and facilitators of adherence to a perioperative physical activity intervention in older adults with lung and gastrointestinal (GI) cancers and their family caregivers (FCGs). Methods: A qualitative analysis of physical therapy/occupational therapy (PT/OT) baseline geriatric/functional assessment and intervention sessions notes were undertaken (N = 34 dyads). Written text documents (N = 6 independent PT/OT notes per dyad) were transcribed into a spreadsheet for coding and thematic analysis. Content analysis qualitative approach was used to identify themes and guide data interpretation. Results: Ten themes for barriers and five themes for facilitators emerged, reflecting barriers to and facilitators of perioperative physical activity adherence. Primary barriers to adherence included comorbid health conditions, physical symptoms, functional limitations, anxiety, other roles and responsibilities, unexpected life events, lack of time and motivation, not accustomed to physical activity, and environment/weather. Facilitators that enabled intervention adherence included physical activity as part of routine, coping strategies, setting goals for motivation, social/family support, and experiencing benefits from walking. Conclusions: Barriers and facilitators to a perioperative physical activity is multidimensional, and focused on social-ecological determinants of health behaviors, including intrapersonal, interpersonal, and environmental factors. Perioperative physical activity interventions for older adults with cancer and their FCGs should integrate strategies to promote self-efficacy, support realistic activity goals, enhance motivation, and optimize social support.