Although it has been show that early detection through mammograms is the most effective way to reduce breast cancer mortality, breast cancer is the leading cause of cancer deaths among women worldwide with survival rates being even lower in low- and middle-income countries as compared to high-income countries. Despite the availability of breast cancer screening programs in Brazil through the public health system, some women do not participate in these programs due to structural and/or inter/intrapersonal barriers. The Community Health Worker (CHW) model is a promising approach to reach these women who have not been reached through other efforts. This paper describes a participatory approach for capacity building of CHWs to promote breast cancer screening among low-income women 50 years of age and older in a southern city in Brazil as a combined effort between two academic institutions, the municipal health care system, and a local non-profit organization. The capacity building program consisted of an 8-hour training focusing on knowledge (e.g., breast cancer and screening) and skills (e.g., communication skills, basic principles of behavior change) to promote breast cancer screening among community members. Pre- and post-test questionnaires assessed changes in breast cancer knowledge and self-perceived knowledge and confidence (N=44). There was a significant increase in objective knowledge regarding breast cancer overall, risk factors, and behavior change strategies between pre- and post-test. There was also a significant increase in self-perceived knowledge and confidence, items related to knowledge about breast cancer, breast cancer early detection methods, and the ability to solve problems between pre- and post-test as well as a significant increase in their confidence to motivate women to get a mammogram. Overall, this study demonstrates the importance of welldeveloped capacity building programs to promote breast cancer screening among health care professionals, especially those with limited educational attainment, such as CHWs.