PROJECT SUMMARY/ABSTRACT The American population is aging at an accelerated pace as the baby boomer generation enters into late adulthood. By the end of 2030, individuals aged 65+ will account for 20.6% of U.S. population, up from 16.9% in 2020 and 12.4% in 2000. In contrast to the growing aging population is a limited amount of public recreational resources dedicated to older adults. Given that older adults usually have abundant free time and quality leisure engagement contributes to healthy aging, there is an urgent need to provide effective leisure services and programs for healthy aging based on rigorous research. Senior centers represent an important public and affordable leisure option for older adults. Through a diverse offering of recreational and healthrelated programs, senior centers have the potential to enhance the health and well-being of older adults. However, there remains a scarcity of research on the impact of senior center on older adults’ health in the United States. Additionally, there are limited scientific guidelines on how to design the physical (e.g., amenities) and social (e.g., programs, staffing) environments at senior centers to effectively promote healthy aging. Therefore, we propose to examine the impact of senior center use on older adults’ health and how senior center’s physical and social environmental attributes affect older adults’ health outcomes over time. The specific aims are: 1) To describe the variation in senior centers’ physical and social environmental attributes in relation to community-level socioeconomic status over time; 2) To assess the association between senior center perception, use, and older adults’ physical and mental health over time for different age groups (≤74 vs. ≥75) and genders; 3) To identify the specific physical and social environmental attributes that optimize health outcomes for different age groups (≤74 vs. ≥75) and genders. The study aims will be addressed by 2 waves of panel data collected using surveys and field observation at approximately 20 diverse senior centers in Southern California. Approximately 75 users will be sampled at each center (i.e., a total of 1,500 users). The study finding will provide important empirical evidence regarding the impact of senior centers on healthy aging and potential disparities in aging-related resources to assist in policy and decision making related to aging. Furthermore, this study will offer direct implications to parks and recreation and public health agencies on how to design and optimize the amenities and programs/services at senior centers to achieve optimal health outcomes for older adults.