bstract:Breast cancer is a malignant neoplasm, an abnormal growth of breast tissue that does not see the surrounding tissue, grows infiltrative and destructive, and can metastasize. Every breast cancer patient experiences side effects from various treatment treatments. This is because the therapy that each patient gets varies and also that cancer sufferers have different genetic backgrounds and different environments. Mastectomy in breast cancer patients can cause many patients to suffer from decreased joint mobility, lymphedema, and limitation in daily activities. These complaints can be overcome with arm exercises. Arm exercises are done to improve circulation and muscle strength and to prevent joint stiffness, preventing lymphedema from occurring. The purpose of this study was to analyze the effect of arm exercises on lymphedema prevention by looking at the value of arm measurements before the intervention and after intervention in the intervention and control groups. The research design was a quasi-experimental study with a total sample size of 32 respondents per group so that the total sample was 64 respondents. The research results were based on the t-test. The independently obtained p=0.001, namely p <0.005, which means that there was a significant effect of the arm measurement value on post-mastectomy breast cancer. It is hoped that this study can be used as education for post-mastectomy patients to improve the lymph flow so that lymph flow obstruction does not occur.