The basic attributes of the urban built environment are an important factor affecting mental health. However, research has rarely distinguished objective and perceived built environment characteristics to explore the associations with older adults' mental health. Based on data of 879 respondents aged 60 or older in Dalian, China, we explored the mediating roles of perceived built environmental attributes in the relationship between objective built environmental characteristics and mental wellbeing by structural equation modelling. Furthermore, to control for residential self-selection, the model was further tested by excluding the participants who self-selected their residences. The results showed that accessibility to daily living service facilities was positively associated with older adults' mental wellbeing through an indirect role of perceived built environmental attributes. The positive direct effect of aggregation of daily living service facilities on mental wellbeing was offset by the negative indirect effects of perceived built environmental attributes. In addition, the street interface density was negatively related to mental wellbeing through indirect effects. The diverse leisure, exercise and landscape facilities, underground parking and presence of elevators within neighborhoods were all positively associated with older adults' mental wellbeing through direct and/or indirect effects. The results were verified after excluding residential self-selection samples. These findings are helpful for evidence-based planning strategies and can provide guidelines on designing neighborhood landscapes and facilities which can further contribute to aging in place policies.