Background and Aim: Incorrect beliefs and negative thinking of society and in the family affect psychiatric patients over the process of treatment, care and recovery. The aim of this study was to investigate the effect of group counseling on the attitude of family caregivers in patients with mental disorders. Materials and Methods: This quasi experimental study was conducted in psychiatric wards of Farshchian Hospital in Hamadan in Iran in 2018. 49 family caregivers were randomly selected to the study. Data were collected using a researcher-made mental attitude questionnaire. At first, family caregivers' attitudes were evaluated; then, they held 4 groups and for each group done 4 sessions of 60 minutes of group counseling. The questionnaire was completed again by the family caregivers immediately after the intervention. Data analysis was done using SPSS software version 16 using descriptive and inferential statistics. Results: The mean of the attitude of the family caregivers before the group counseling was (12.59 ± 13.49). The mean of the attitude score of family caregivers after group counseling was (24.45 ± 8.32). Paired t-test showed that the attitude score of caregivers increased significantly after group counseling (p <0.001). Discussion and Conclusion: The results of the study indicate that group counseling improves the attitude of family caregivers towards mental illness. Therefore, it is recommended that psychiatric nurses use this method to educate families of mental patients.