Background: Family plays a crucial role in improvement and treatment continuation of individuals under methadone treatment. Understanding, supporting, and accepting the patient by the family and friends are factors influencing the treatment and rehabilitation process. Objectives: The aim of this study was to determine the effect of family counseling on acceptance and support rates of patients under MMT. Methods: In this quasi-experimental study, 50 patients (25 in the intervention group and 25 in the control group) under methadone treatment, in addiction treatment centers, in Kermanshah were selected through cluster sampling and randomly divided into 2 intervention and control groups. Data collection from the patients in both groups was conducted before and 4 weeks after last session intervention using family support and acceptance questionnaires. Intervention for patients' family members (2 primary members for each patient) was held as a group-counseling meeting using Michael Free's methodology. Patients in the intervention and control group received only the usual care of the center. Data were entered into SPSS software (version 18) and analyzed using appropriate statistical tests. Results: The family social support rate for the patients before and 4 weeks after counseling in the control group changed from