An optimal adjuvant endocrine therapy is yet to be established for post menopausal women with hormone receptor positive breast cancer. The current therapeutic options include initial, switch, and extended adjuvant therapies. We aimed to determine the most cost-effective therapeutic option using the clinical decision analysis method. It was suggested that aromatase inhibitor monotherapy in initial adjuvant therapy is the most cost-effective and optimal adjuvant endocrine therapy for post menopausal women with hormone receptor-positive breast cancer.