Older adults with lower limb osteoarthritis (LLOA) are highly dependent on their physical and social environment for being physically active. Longitudinal data from 2286 older adults (M age = 73.8 years; 50.3% female) in six European countries were analyzed using cross-lagged Structural Equation Modeling (SEM) and multi-group SEM. In cross-sectional analyses, neighborhood resources were associated with physical activity (r = 0.26;p <.001) and social participation (r = 0.13;p =.003). Physical activity at follow-up was associated with neighborhood resources, with this relationship mediated by social participation in people with LLOA (β = 0.018;p =.013). To promote future physical activity, opportunities to socially engage in neighborhoods need to be targeted primarily to people with LLOA.