The incidence of breast cancer in 2018 in Samosir Regency was 20 cases, while in Cinta Dame Village in 2019 there were 2 people at an advanced stage, 1 person died and 1 person was undergoing chemotherapy. The number of women of childbearing age in Cinta Dame Village (aged 15–49 years) is 497 people. Objectives; to determine what factors were related to the behavior of childbearing age women in performing breast self-examination (BSE). Method; this research was a quantitative analytic type which is cross-sectional. The population were all women of childbearing age were 497 people with a sample using the simple random sampling technique were 83 people. Data analysis used univariate and bivariate analyses with chi-square test statistics. Result; the results of the analysis showed that p-value of each variable includes knowledge obtained .000, attitudes obtained by p-value was.000 and family support obtained by p-value was .000. Conclusion; the conclusion showed that influence of knowledge, attitudes, and family support on BSE behavior were found.