This study aimed to investigate the patient outcomes and cost of breast cancer patients treated with chemotherapy. A retrospective-cohort study was performed in patients who were diagnosed with breast cancer and received cytotoxic drugs at the National Cancer Institute (NCI), Thailand, since 2001 with 2-year follow-up. Of 1,088 patients, 296 were selected. Most patients were between 41-45 years old (21.3%), in agricultural sector (36.5%), with stage II disease (71.3%) and used FAC (5-fluorouracil, adriamycin and cyclophosphamide) regimen (47.3%). Duration of treatment and number of laboratory tests ranged between 90-120 days and 21-30 tests, respectively. In this study, for stage I, regimen AC (adriamycin and cyclophosphamide) consumed the least resource use, i.e. 80.73 days of treatment, 21.09 laboratory tests and 25.09 patient visits, and therefore resulted in the lowest total cost of treatment, $249.67. A similar result was demonstrated for stage II that was regimen AC had minimal duration of treatment (95.67 days), laboratory tests (24.91), number of patient visits (30.31), cost of cytotoxic drugs, ($106.95) and total cost of treatment ($290.34). All patients were discharged with no node positive and some patients continued follow-up with laboratory tests or continued hormonal therapy. From this study, it can be concluded that patients with stage I and II adjuvant breast cancer who have no risk of heart disease can therefore start the treatment with AC regimen.