Background <p>Depression is a significant mental health concern among older adults and is often exacerbated by environmental and social factors. Despite rapid global urbanisation and ageing populations, few empirical studies have explored the associations between age-friendly urban environments and depression in older populations. This study investigated the relationship between the World Health Organization (WHO) Age-Friendly Cities Framework and depression among older adults in South Korea, aiming to derive urban planning and policy implications for healthy ageing.</p> Methods <p>We analysed data from the 2020 National Survey of Older Koreans, which included 9,920 individuals aged 65 and older. Depression was measured using the Korean version of the Short-Form Geriatric Depression Scale (SGDS-K). Eight domains of the WHO Age-Friendly Cities Framework—such as park accessibility, housing convenience, social participation, and access to information—were used as independent variables. Sociodemographic characteristics were included as covariates. Associations between environmental factors and depression were examined using multiple logistic regression.</p> Results <p>Several urban environmental factors were significantly associated with a reduced likelihood of depression. These included better accessibility to parks (OR = 0.815), living in elderly-friendly housing or adequate housing (no elderly-friendly features) (OR = 0.482 and OR = 0.419), participation in leisure activities (OR = 0.763), perceived social respect (OR = 0.690), and engaging in volunteer activities (OR = 0.396). In contrast, difficulty in accessing life information services was associated with an increased risk of depression, particularly among those experiencing the greatest difficulty. Access to healthcare institutions was also linked to a higher risk of depression, especially for those living within a 10-minute walking distance. No significant associations were found for public transportation or participation in elderly employment programs.</p> Conclusions <p>This study highlights the critical role of age-friendly urban environments in supporting the mental health of older adults. Urban planning should prioritise accessible green spaces, elderly-friendly housing, inclusive leisure opportunities, and improved access to life information. Promoting social respect and volunteer engagement can further enhance emotional well-being. These findings provide empirical support for implementing the WHO Age-Friendly Cities Framework as a strategic approach to reducing depression and promoting healthy ageing in urban contexts.</p>