Mother-infant interactions are a proximal process in early development and may be especially salient for children who are at risk for social difficulties (i.e. infant siblings of children with autism spectrum disorder). To inform how indices of maternal behaviors may improve parent-mediated interventions designed to mitigate autism spectrum disorder risk, the present study explored maternal social responsiveness ratings and social behaviors during dyadic play interactions. Dyads were recruited from families with at least one older child with autism spectrum disorder (high-risk group, n = 90) or families with no history of autism spectrum disorder (low-risk group, n = 62). As part of a prospective study, interactions were coded when infant siblings were 6, 9, and 12 months of age, for gaze, affect, vocalizations, and multimodal bids or responses (i.e. social smiles). Maternal social responsiveness was indexed via the Social Responsiveness Scale. Mothers in both risk groups had comparable Social Responsiveness Scale scores and social behaviors during play. Two maternal behaviors emerged as positive correlates of infant social behaviors and are thus of high relevance to parent-mediated interventions. Specifically, more maternal positive affect and the use of multimodal bids or responses were associated with more infant positive affect, vocalizations, gaze to face, and multimodal bids or responses.