Background <p>The global elderly population is growing rapidly, and physical inactivity among the elderly remains a leading cause of morbidity and mortality. Implementing structured, theory-driven behavior change strategies that foster social support is essential for successful health promotion among the elderly. This study aims to evaluate whether a community-based social marketing campaign can effectively enhance physical activity, social support, and self-efficacy in the elderly. </p> Methods <p>This study is a parallel cluster-randomized controlled trial protocol. A three-month community-based social marketing campaign will be implemented for 500 elderly aged 65 to 75 living in Rasht, Guilan Province, Iran. The intervention will be delivered through eight randomly selected CHSC, while the remaining eight centers will serve as controls and continue routine care. Social support and self-efficacy as primary outcomes will be assessed at 3 months, and physical activity as a secondary outcome at 6 months after the intervention. Randomization will be performed at the cluster level using block randomization to reduce contamination between groups.</p> Discussion <p>This study has the potential to demonstrate the effectiveness of a structured social marketing campaign in improving key determinants of physical activity among the elderly. It also seeks to empower stakeholders and the elderly themselves to actively participate in planning, implementing, and sustaining health promotion initiatives aimed at active aging and promoting physical activity.</p> Trial registration <p>Iranian Registry of Clinical Trials: IRCT20240429061582N1 (Registered on May 22, 2024). <a href="https://irct.behdasht.gov.ir/trial/76535">https://irct.behdasht.gov.ir/trial/76535</a>.</p>