Children with autism spectrum disorder (ASD) are at considerable risk for difficulties with emotion regulation and related functioning. Although it is commonly accepted that parents contribute to adaptive child regulation, as indexed by observable child behavior, theory and recent evidence suggest that parenting may also influence relevant underlying child physiological tendencies. The current study examined concurrent associations between two elements of parental socialization of emotion and measures of both sympathetic and parasympathetic nervous system activity in 61 children with ASD aged 6 to 10 years. To index parental socialization, parents reported on their reactions to their children’s negative emotions, and parental scaffolding was coded from a dyadic problem-solving task. Children’s baseline respiratory sinus arrhythmia (RSA), electrodermal reactivity (EDA-R), and RSA reactivity in response to challenge were obtained as measures of the children’s physiological activity. Regression analyses indicated that supportive parent reactions were related to higher child baseline RSA, a biomarker of regulatory capacity. Fewer unsupportive parent reactions and higher quality scaffolding were associated with higher EDA-R, a physiological index of inhibition. The identification of these concurrent associations represents a first step in understanding the complex and likely bidirectional interplay between parent socialization and child physiological reactivity and regulation in this high-risk population.