Women and the poor are disproportionately affected by common mental disorders (CMD), and women in low income countries are particularly at risk. Social capital may explain some of the geographical variation in CMD, but the association between social capital and CMD in low income countries has rarely been studied. This paper aims to explore the relationship between individual and ecological measures of social capital and maternal CMD in four low income countries. Cross-sectional data from the Young Lives (YL) study with information across 234 communities in Peru, Ethiopia, Vietnam and Andhra Pradesh (India) were used. The mental health of mothers of one-year-old children (n=6909), and the individual cognitive and structural social capital of all respondents was assessed. Ecological social capital was calculated by aggregating individual responses to the community level. Multi-level modelling was used to explore the association between individual and ecological (community level) social capital and maternal CMD in each of the four countries, adjusting for a wide range of individual and community level confounders. The analysis shows that individual cognitive social capital is associated with reduced odds of CMD across all four countries. The results for structural social capital are more mixed and culturally specific, with some aspects associated with increased odds of CMD. This suggests that structural social capital has context-specific effects and cognitive social capital more universal effects on maternal CMD.