The elderly's needs and preferences for public open space seem different from who are not in elderly time; also, ageing requirements should be taken into consideration to improve older adults' active life. In this respect, creating active ageing requires a new approach to engage older citizens in outdoor environments viewed as healthy and sustainable by the seniors. This study aims to identify the elders' preferences, especially their use of public open spaces (POSs) in Iranian urban neighbourhoods as well as identifying the association among the factors. The research was conducted in two steps; First, Grounded Theory (GT) by employing 64 semi-structured interviews in POS and then data analyzed to extract the main concepts. Second, a survey was conducted through a self-administered questionnaire based on extracted items, to which 420 elderly people responded. Partial least squares-Structural Equation Modelling (PLS-SEM) was employed for data analysis and developing the model. The results indicated that the process in environments (social environment, cultural environment and sense of belonging) - as the non-physical dimensions of POSs- significantly influence the demands of the elderly in outdoor environments. Among physical features of POSs, the place functions (access to amenities, urban landscape, and environmental cleanness), as well as place preferences (crime security, fear of falling security and the elders' image), are more likely to meet the elders' needs in urban spaces. These findings also revealed a significant causal relationship between the factors adopted from the developed model. The findings will highlight POSs both theoretical and practical implications for urban planners and designers as well as policy-makers.