Few studies have examined interventions or therapeutic processes that may help parents of children with Autism Spectrum Disorder (ASD) manage their stress. This study examines the impact of a brief Acceptance and Commitment Therapy (ACT) group intervention, led by parents, among a cohort of 33 mothers of children with ASD. Changes in ACT process measures (psychological flexibility, cognitive fusion, values) were evaluated at pre, post, and 3 months following the intervention. Mothers reported significant improvement post-intervention in psychological flexibility, cognitive fusion, and value-consistent activities in multiple life domains, including parenting, relationships, and self-care. These improvements were maintained at follow-up. The results provide preliminary evidence that improvements observed in depression and stress may be mediated by cognitive fusion and action-values consistency.