The aim of this study was to investigate the effects of adding group acceptance and commitment therapy (ACT) to adults diagnosed with obsessive compulsive disorder (OCD) who were already on an optimal dose of selective serotonin reuptake inhibitors (SSRIs). Forty-six Iranian women, on SSRIs, were randomized to group ACT + SSRI or continued SSRI conditions. SSRI dosages stayed stable during the study. Assessments included the Structured Clinical Interview (SCID-I), Yale-Brown Obsessive-Compulsive Scale Self report (Y-BOCS-SR), Beck Depression Inventory-II (BDI-II), Ruminative Response Scale (RRS), and Acceptance and Action Questionnaire (AAQ-II). The results showed significant reductions on the Y-BOCS-SR and BDI-II in both conditions at posttreatment with significantly greater reductions in the ACT + SSRI condition at follow-up. The RRS and AAQ-II saw significant improvements in the ACT + SSRI condition at posttreatment and follow-up compared to the SSRI condition. Results provide cross-cultural support for group ACT as a treatment for OCD and as a successful adjunct to SSRI treatment.