Summary Individuals living in socioeconomically deprived inner cities have disproportionately high rates of cardiovascular disease, cancers, Type 2 diabetes and obesity, which have stress- and physical activity-related etiologies. Previous research on the urban built environment suggests that parks may reduce stress and increase physical activity. Yet, the causal health relationships have been difficult to establish due to reliance on cross-sectional designs, coarse exposure assessment, limited health effects data and neglect of negative aspects of green space (e.g., litter, noise). This study will capitalize on an upcoming natural experiment in five low-income neighborhoods in Detroit, MI involving the ecological restoration of unmaintained parks to grassland meadows. Five control park neighborhoods were matched on demographic and built characteristics. This longitudinal study will include participants (n=590 after attrition) from ten intervention/control park neighborhoods with baseline measurement then annual measurement for three years post- restoration. Our study will be the first natural experiment to examine the impact of ecological restoration with individual-level measurement of visual/auditory exposure (e.g., greenery, birdsong) to green space on health. We will go beyond the usual objective measure of physical activity (GPS/accelerometer) in park studies to include a validated stress biomarker (salivary cortisol) and cardio-metabolic indicators (BMI, blood pressure, hip-to-waist ratio, C-reactive protein and A1C). The question to be answered is: Does ecological restoration of abandoned parks into grassland meadows and bird habitats increase nearby resident’s physical activity, lower their stress, and improve their cardio-metabolic health? We propose three aims. Aim 1: Establish the effect of ecological restoration of parks on physical activity from baseline through 3-years post-restoration, using a non-randomized design. Aim 2: Illuminate the stress reduction potential of restored parks. Aim 3: Evaluate the effect of ecological restoration on downstream cardio-metabolic health outcomes. Understanding the role of ecological restoration on health will provide the unique opportunity to inform replication, scalability and generalizability for cities managing park resources in low-income neighborhoods. Our findings will be vital in the development of policies needed to mitigate pervasive socioeconomic disparities in obesity, Type 2 diabetes, cancer, and cardio-metabolic health.