In Hong Kong, an increasing number of outdoor exercise facilities have been established in public open spaces to promote physical activity (PA) in older adults. However, no intervention is dedicated in educating the public on how to make use of these resources to fulfil the PA guidelines based on behavioural change theory. This study has two phases, phase one aims to describe the participatory development of the intervention, and phase two is the evaluation of a public outdoor exercise facilities-based PA education intervention for community-dwelling older adults. A mixed-methods participatory design was used to evaluate the impact of the intervention. PA behaviour was assessed as the fulfilment of the PA recommendations by World Health Organization, and the Rapid Assessment of Physical Activity (RAPA) scale at baseline, immediately, and 3 and 6 months post-intervention. Psychosocial constructs and physical assessments were carried out at both pre- and post-intervention. Individual in-depth interviews were conducted at post-intervention. Forty-seven participants were enrolled in the intervention. The average adherence rate was 90.87%. PA significantly increased after the intervention and remained elevated for the following 6 months. Post-intervention, the qualitative findings supported the quantitative findings at both the individual and social levels. However, findings regarding the change in participants' usage of environmental resources were divergent. The intervention was well-received by the participating older adults, as reflected by the high adherence rate. Both quantitative and qualitative data demonstrated the overall impacts of the intervention for creating sustainable changes in PA behaviour. © 2021 John Wiley & Sons Ltd.