Parents of children diagnosed with autism spectrum disorder (ASD) report higher levels of stress and other negative affective states than parents of typically developing children. One important resource in managing these heightened levels of negative affect is emotion regulation, which in turn depends upon the ability to recognize and understand one's own and others' mental states (referred to as mentalization or reflective functioning). In this study, parents of children with ASD either participated in a mentalization‐based group intervention (N = 36) or a delayed treatment (N = 28). Compared to delayed treatment participants, parents in the mentalization‐based group had increases in reflective functioning and in the belief that emotions can change. Moreover, they reported decreased behavioral and emotional symptoms in their children, and greater parental self‐efficacy. These preliminary findings support previous studies, which have shown that mentalization‐based interventions for parents lead to positive outcomes, and suggest that these findings may apply to a diverse population of parents such as those of children with broader autism phenotype or children with different neurological disorders. Further studies to evaluate the effects of the intervention are recommended. Autism Res 2019, 12: 1077–1086. © 2019 International Society for Autism Research, Wiley Periodicals, Inc. Lay Summary In this study, parents of children with ASD participated in a group intervention designed to increase their awareness of mental states (their own and their children's) and to enhance their emotion regulation. Compared to delayed treatment parents, those in the intervention group showed increased awareness of developmental states, and reported increased belief that emotions can change and decreased levels of behavioral and emotional symptoms in their children.