Background: Marital life is based on effective reciprocal relations such as quality of communications with the spouse’s family. Objectives: The present study aimed to investigate the effectiveness of cognitive-behavioral group therapy on negative feelings of the women toward their husband’s family and marital conflicts. Methods: This is a quasi-experimental study with a pretest-posttest design and follow-up with a control group. The statistical population included all women referring to Rahgosha Consultation Center in the town of Tiran (due to marital conflicts) in 2018. Thirty samples were selected using a convenient sampling technique. Then, the samples were randomly divided into two groups of experimental (15 women) and control (15 women). Women’s negative feelings toward the husband’s family and marital conflicts questionnaires were used to collect data. The experimental group received seven ninety-minute sessions of cognitive-behavioral group therapy. Finally, a posttest was performed for both groups. Moreover, the follow-up stage was administered a month after the posttest on both groups. Mean and standard deviation were used to analyze the data at descriptive statistics, and MANCOVA was used at the inferential statistics level through SPSS21 software. Results: Cognitive-behavioral group therapy could effectively decrease both the women’s negative feelings toward their husband’s family and marital conflicts (P < 0.05). Conclusions: This study demonstrated that cognitive-behavioral group therapy can be applied to decrease negative feelings toward the husband’s family and to address marital conflicts.