The COVID-19 pandemic emphasized the importance of accessible outdoor spaces for mental well-being. This study investigates the relationship between exposure to urban green spaces and levels of anxiety, depression, and stress among 2,000 adults in three major metropolitan cities. Using GIS mapping and standardized mental health scales (GAD-7, PHQ-9), we found a significant negative correlation between proximity to green areas and reported psychological distress (p < 0.01). The results highlight the role of urban planning in mental health promotion, suggesting that equitable distribution of green zones could serve as a preventive public health measure.