Abstract: Objective To evaluate the efficacy and toxicity of trastuzumab plus endocrine therapy as maintenance therapy after first-line chemotherapy plus trastuzumab for HR-positive and HER-2-positive metastatic breast cancer. Methods Patients with HR+／HER-2+ metastatic breast cancer receiving first-line chemotherapy and trastuzumab and sequentially continued endocrine therapy with ongoing trastuzumab as maintenance therapy were enrolled in this study. The clinical data was retrospeetively collected and efficacy and toxicity of the maintenance trastuzumab and endocrine therapy was analyzed. Response to maintenance therapy was assessed by RECIST criteria 1.1 and toxicity was evaluated according to Common Terminology Criteria for Adverse Events （CTCAE） v4.0. The prognosis was analyzed according to the follow-up data. Results Thirty-one patients were enrolled. The median progression-free survival of maintenance therapy was 12.0 months （95％CI： 5.4-18.6 months）. The maintenance regimen achieved response rate of 26.9％ and disease control rate of 88.5％. The most common adverse events were mild， including fatigue （19.4％）， hot flashes （16.1％） and nausea and vomiting （9.7％）. Conclusion Adding maintenance endocrine therapy to ongoing trastuzumab upon the completion of first-line chemotherapy plus trastuzumab might improve clinical outcomes for HR+／HER-2+ metastatic breast cancer， and the regimen was well tolerated.