This study was undertaken to examine the effectiveness of group acceptance and commitment therapy upon perceived social support and social adjustment of mothers of children diagnosed with autism in Dezful in 2019. This quasi-experimental research had a pretest-posttest control group design. The statistical population of the study comprised all mothers of children with autism spectrum disorder in Dezful from among whom 30 individuals were selected through purposive sampling method and based on inclusion criteria. The subjects were randomly put into two groups of experimental (N=15) and control (N=15). The experimental group received the intervention in eight 90-minute sessions and the control group remained on the waiting list. The research instruments included Multidimensional Scale of Perceived Social Support (Zimet, Dahlem, Zimet & Farley, 1988) and the Adjustment Inventory (Bell, 1962). Data were analyzed using ANCOVA and MANCOVA. Results showed that there was a significant difference between the two groups in perceived social support and social adjustment at the posttest stage (p<0.001). The results indicated that ACT had a positive effect on perceived social support and social adjustment of mothers of children diagnosed with autism. Due to the use of metaphors in ACT as well as emphasis on values in this therapy, it leads to increased perceived social support and social adjustment; therefore, it is suggested that ACT be considered for mothers of children with autism spectrum.