The Young Lives project in Vietnam allows the examination of the relationship between maternal social capital and child well-being. With a sample of 1,953 mothers of one-year-olds and 954 mothers of eight-year-olds across five provinces, this study examines whether maternal social capital is associated with child health. This study found low levels of structural social capital (associational life) and citizenship and high levels of cognitive social capital (trust, etc) and support. While poorer women have even lower levels of structural social capital than their better-off peers, patterns across rural and urban areas are similar. Maternal social support and high cognitive social capital show the most consistent associations with child health, while associations between maternal social capital and child health are stronger among one-year-old children than among eight-year-olds, with the exception of child mental health and risk of life-threatening illness. The most consistent associations were seen with the mental health of eight year- olds, with all four indicators of social capital being significantly associated with mental health after other variables have been controlled for. Lastly, there was some evidence to suggest that active membership of formal organisations in Vietnam may be damaging to the health of eight-year-olds but not one-year-olds, with active participation in formal groups being significantly associated with an increase in stunting among eight-year-olds.