Breast cancer not only occurs in developed countries but also in developing countries such as Indonesia. Breast cancer ranks 8th out of all cancers in Indonesia. Breast cancer is also a major concern, because it is the most common type of cancer affecting women. This study aims to determine the effect of breast self-examination health education on knowledge, attitudes, and actions of adolescent girls at SMK Kader Bangsa Palembang. This research method uses a quasi-experimental design with pretest posttest. The population was adolescents with menstrual cycles to 7-10 days with a total sample of 26 respondents who met the inclusion criteria. The test used was the Wilcoxon Sign Runk Test with p<0.05 using a computer. The results showed that health education on breast self-examination (SADARI) had an effect on knowledge p value (0.000<0.05), attitude p value (0.003)<(0.05), action p value (0.004)<(0.05). Conclusion There is an effect of health education on breast self-examination (SADARI) on knowledge, attitudes, and actions of adolescent girls at SMK Kader Bangsa Palembang. Suggestions are expected to schoolgirls can be made as a stewardship of SADARI techniques to detect early signs and symptoms of breast cancer.