Background & aim: The theory-based counseling can motivate clients to perform breast self-examination (BSE), which is an easy, safe and cost-effective method. This  study evaluated the effect of group counseling based on the Protection Motivation Theory (PMT) on perceived severity, perceived sensitivity, and perceived reward of BSE behavior.Methods: This clinical trial was conducted on 66 women aged 30-69 years referred to healthcare centers of Mashhad, Iran. The subjects were selected by convenience sampling and then assigned randomly in two intervention and control groups using time block. Data were collected using a demographic characteristics and a self-structured questionnaire on women's participation in BSE behavior based on the PMT. The intervention group received four weekly 60-minute group counseling sessions in groups of 8-10 people based on the PMT. The control group received the usual care. Perceived severity, perceived sensitivity, and perceived reward of BSE behavior was measured in two stages before and two months after the end of the intervention. Data were analyzed by SPSS V. 22) using independent and paired t-test, Man-Whitney, Chi-square, and Fisher exact tests.Results: The total score of PMT was not significant in the two groups before the intervention. But after the intervention, mean score of the perceived sensitivity (25.62±3.78 vs. 20.86±2.29), perceived severity (21.06±3.58 vs. 16.06±3.41) and perceived reward (4.83±1.53 vs. 17.16±2.79) was significantly different in the intervention and control group (p<0.001).Conclusion: Group counseling based on the PMT by overcoming fear and increasing motivation in women can increase BSE behavior in order to prevent breast cancer.