Objective: The aim of the study was to observe the cardiac toxicity caused by diferent doses of epirubicin in the adjuvant treatment of breast cancer and to evaluate the long-term eficacy.Methods:The 180 cases of breast cancer patients received epirubicin based adjuvant chemotherapy. The patients were randomly assigned to high-dosage group (90 mg/m2), medium-dosage group (70 mg/m2) and low-dosage group (50 mg/m2), the primary endpoint was cardiac toxicity. The secondary outcomes were the 5-year overal survival (OS) and 5-year disease-free survival (DFS).Results: During chemo-therapy, the clinical symptoms such as palpitation, dyspnea and paroxysmal nocturnal dyspnea occurred in 6 patients with the high-dosage group, 4 patients with the medium-dosage group and 3 patients with the low-dosage group. The number of patients who had changed in electrocardiogram (ECG) was 7, 5 and 4 in three groups, respectively. The echocardiographic showed each group had only one case with LVEF 0.05). In the three groups, the 5-year DFS rates were 73.3% (44/60) in high-dose group, 53.3% (32/60) in medium-dose group and 41.6% (25/60) in low dose group. The 5-year OS rates were 85.0% (51/60), 68.3% (41/60) and 58.3% (35/60) in three groups, respectively. The diferences were statisticaly significant (P < 0.05).Conclusion: The high-dose epirubicin in adjuvant chemotherapy with CEF (cyclophosphamide, epirubicin and fluorouracil) regimen could improve the 5-year OS rate and 5-year DFS rate on patients of breast cancer. The cardiotoxicity was mild-moderate and wel tolerated.