The purpose of the study was to develop organization-based core performance measures (CPMs) for breast cancer patients treated in hospitals that participated in cancer quality improvement programmes in Taiwan. CPMs were developed in three stages that included a preparation, a consensus building stage, and two stages of stakeholder feedback. Three criteria and seven subcriteria were applied in the development process. Indicators listed in a Delphi questionnaire were based on a literature search, indicators developed by relevant institutions and discussion by authors. Each indicator needed to meet inclusion criteria as a final indicator. Evidence-based guidelines, expert opinions from panel group, 27 hospitals and empirical data were all applied to develop and revise the core measures. Fifteen out of 28 indicators were selected and modified after the three stages. There were two pre-treatment indicators for screening and diagnosis, nine treatment-related indicators, and four monitoring-related indicators. Six indicators were supported by evidence level I, and four indicators by level II evidence. The CPMs for breast cancer can be developed systematically and be applied for internal quality improvement and external surveillance. Our experience can be extended to other cancer sites and adapted to link with pay for performance or certification program in cancer care.