Despite parks have been widely recognized as key environmental sites by building free and accessible physical activity (PA) resources in nature, evidence suggests that less than one third of surveyed or observed elderly park visitors use parks for PA. Additionally, little is known about older adults’ PA patterns in parks and the potential attributes of their park-based PA. Based on social ecological approach, the attributes of park-based physical activity can be explained in terms of types of PA areas, and the psychosocial and perceived park environmental factors (Sallis et al., 2006). Comprehensively understanding park-based PA among older adults and the relevant attributes could contribute to developing a conceptual framework of park-based PA, as well as guiding the evidence-based policies aimed at creating user-friendly environments for elderly park users. The overall purpose of the dissertation is to get a picture of older adults’ PA in parks and the underlying mechanism of their park-based PA. Based on the overall research question and the limitations in previous studies, there are three specific research questions with several sub-questions, including: Q1: How about older adults’ PA observed in PA areas in Leipzig and Hong Kong parks? Q2: Is there association between types of PA areas and park-based PA (i.e., number of active elderly visitors) for elderly park visitors in Leipzig and Hong Kong? and Q3: Is there association between the psychosocial and perceived park environmental factors and park-based PA for elderly park visitors in Leipzig and Hong Kong?