BackgroundIran has experienced a very fast fertility transition. The process of demographic transition, coupled with modernization, has had considerable consequences for the structure and function of families. There is rising concern in Iran about a potential decline in family care and support for older people as a result of these changes. The main aim of this study was to provide a benchmark by examining current associations between family factors and older people’s social support, both perceived and received.MethodsA cross-sectional survey of a random sample of 644 people aged 60 + years resident in Tehran was conducted using stratified cluster random sampling method in 2015. Outcome variables were perceived social support, as measured by Social Provision Scale, and received instrumental social support. Multilevel mixed-effects models were used to examine the hypotheses.ResultsThe analyses showed that most of the family factors measured, including family size (p = 0.01), living arrangements (p = 0.05), and amount of contact with family members (p = 0.001) were associated with older people’s receipt of instrumental social support. Living arrangements and quality of relationships with family members were associated with older people’s perceptions of social support (p < 0.001). Also, a significant gender interaction was found in associations between family size and SPS (p = 0.03). Having a large size family was positively associated with higher SPS for women (Coef. = 3.9, p = 0.009) but not for men (Coef. = -0.4, p = 0.7).Conclusionfindings of this study support the premise that most of family factors play an important role in provision and perception of social support for Iranian older people. Further policies should mostly be selective of those at higher risk of low support such as widowed, childless, those living alone, having poor relationship with their relatives and those with worse health status. The results of this study may be utilized to target older populations who are at higher risk of low support with innovative programs that focus on building social networks and enhancing social support.