Outdoor walking has considerable benefits for healthy ageing and older adults are recommended to walk regularly. However, older adults living in high-deprivation areas walk less than those living in low-deprivation areas. Previous research has shown that the characteristics of neighbourhood green spaces (i.e., proximity, attractiveness, size, and number) may influence outdoor walking. This study examines spatial inequalities in the characteristics of neighbourhood green spaces in high- versus low-deprivation areas and their possible influences on disparities in older adults’ outdoor walking levels. For this purpose, it included a sample of 173 participants (≥65 years) and used secondary data and a geographic information system (GIS) to objectively measure neighbourhood green spaces characteristics. Geographic positioning system (GPS) technology was used to objectively measure outdoor walking levels. Data on participants’ personal characteristics were collected by questionnaire. The results indicate that one characteristic of neighbourhood green spaces (i.e., size) is positively related to outdoor walking levels. They show that inequalities in neighbourhood green spaces’ size in high- versus low-deprivation areas may influence disparities in older adults’ outdoor walking levels. Despite inequalities in other neighbourhood green space characteristics (e.g., proximity, attractiveness, and number) in high- versus low-deprivation areas, no relationship was found between these neighbourhood green space characteristics and participants’ outdoor walking levels. Enhancing the distribution or creation of large neighbourhood green spaces (e.g., through creating green space networks) may enhance outdoor walking among older residents, especially in high-deprivation areas.