<p>Maternal stress is a growing societal concern, with implications for both maternal wellbeing and infant development. One of the mechanisms by which maternal stress is thought to impact infant development is by shaping the development of the infant gut microbiome. Here, we examined how measures of maternal stress and social support were associated with alpha diversity, beta diversity, and relative abundance of individual bacterial taxa in the gut microbiota at 12 months of age in a community-based sample of infants and their biological mothers (<i>n</i> = 34) from New York. Maternal social support was negatively associated with alpha diversity of the infant gut microbiota and was associated with abundance of bacteria from several genera. We did not find associations between caregiver perceived stress and markers of infant gut microbiota diversity or composition. Results suggest that greater social support for new parents may be associated with infant health via changes in the diversity and composition of the infant gut microbiota.</p>