The present study sought to investigate the effectiveness of Bowen-based differentiation therapy on the developmental functioning of families and the fusion of mothers with children aged 3-14 years with autism spectrum disorder in Abadeh city in 2022. This quasi-experimental research had a pre-test, post-test control group design. The statistical population comprised all mothers with children aged 3-14 years diagnosed with autism based on DSM-5 criteria and the GARS-2 diagnostic test, whose children were under training at Hazrat Abbas Rehabilitation Center in 2022. Thirty mothers were purposefully selected and randomly assigned to experimental and control groups. The research tools included the Developmental Family Functioning Assessment Questionnaire (DFFAQ) and the Differentiation of Self Inventory-Revised (DSI-R). Participants in the experimental group received ten 60-minute group sessions of Bowen-based differentiation therapy. The results, analyzed using SPSS software and covariance analysis, showed that Bowen-based differentiation therapy significantly improved the developmental functioning of families and the fusion of mothers with children with autism (p<0.05). Thus, this therapeutic approach can be effectively used to enhance family functioning and parent-child relationships in families with children with autism.