Scholars have not yet explored the relationship between community social capital and self-rated health (SRH) among older adults in China in depth, including potential moderators in this relationship. In response to this gap, this study aimed to investigate the association between community social capital and SRH among urban Chinese older adults and the moderating roles of instrumental activities of daily living (IADLs) and smoking. We used a quota sampling method to recruit 800 respondents aged 60 years and older from 20 communities in Shijiazhuang and Tianjin, China. SRH was used as the dependent variable. Binary logistic regression models with interaction terms were used to analyse the data. The results showed that trust (a cognitive social capital indicator), volunteering (a structural social capital indicator) and family social capital were significantly associated with SRH when controlling for other social capital indicators and covariates. Difficulties with IADL and smoking significantly moderated the association between community social capital and SRH. Cognitive social capital was only positively associated with SRH health among respondents who did not experience difficulty with IADLs. The positive association between citizenship activities and SRH was only significant among those who experienced difficulty with IADLs. The number of organisational memberships was negatively associated with SRH among respondents with a history of smoking. Volunteering was positively associated with SRH in respondents with a history of smoking. These findings highlight the important role of social capital in promoting SRH among older adults in urban areas of China and notably identify within-population heterogeneity in the associations between social capital and SRH. This study offers insights useful for developing social capital policies and interventions to meet the specific social needs of older adults with varied levels of difficulty with IADLs and health behaviours.