This study investigated moderating effects of psychosocial factors on the association between walkability and physical activity (PA) in 433 Belgian older adults. Furthermore, main effects of psychosocial factors on PA were determined. No moderating effects were observed for the associations between walkability and transport walking, or moderate-to-vigorous PA (MVPA). Walkability was positively associated with recreational walking in those with high self-efficacy. Regarding main effects, benefits and social norm were positively associated with recreational walking. Benefits were positively and barriers were negatively associated with MVPA. There were no significant main effects for transport walking. The overall lack of moderation suggests that environmental interventions might enhance all older adults' transport walking and MVPA. Recreational walking might be enhanced by simultaneously targeting self-efficacy and neighborhood environmental factors.