Objectives Service accessibility plays a pivotal role in older adults’ mental health. However, accessibility measures used in previous studies are either objective or perceived. This study aimed to integrate both objective and perceived measures of service accessibility to explore the relationship between environmental cognition on service accessibility and mental health in older adults and the pathways. Methods We used both questionnaire data collected from 2,317 older adults in Hong Kong and geographical data to explore the direct and indirect effect of environmental cognition (i.e. positive, negative, and matching evaluation) relating to service accessibility on mental health and two pathways (i.e. physical activity and sense of belonging) based on a structural equation model. Results Physical activity mediated the positive relationship between non-negative perceptions toward access to convenience stores, leisure facilities, clinics, community centers, places of worship and mental health. Sense of community can significantly mediate the positive relationships between non-negative perceptions toward all 10 types of services and mental health. Conclusion This study provides an empirical contribution to environmental cognition theory and person-environment fit theory; its findings have implications for urban planning policy.