Background: HER2-positive metastatic breast cancer (BC) has a high risk of brain metastases (BM), leading to poor survival. Small molecule tyrosine kinase inhibitor (TKI) with enhanced penetrability to the blood brain barrier combined with capecitabine have demonstrated promising clinical outcomes in HER2-positive metastatic BC patients with untreated (such as lapatinib) or previously treated (such as neratinib) BM. The randomized phase III PHOEBE trial has proved better efficacy of pyrotinib, an irreversible pan-HER receptor TKI, versus lapatinib when in combination with capecitabine in HER2-positive local relapsed or metastatic BC. This study was conducted to investigate the efficacy and safety of pyrotinib plus capecitabine in HER2-positive metastatic BC patients with BM. Methods: In this multicenter phase II trial (NCT03691051), eligible patients received pyrotinib 400 mg orally once daily without breaks and capecitabine 1000 mg/m² orally twice daily for 14 days followed by 7 days off. Treatment was continued until disease progression or intolerable toxicity. Prior HER2 TKIs were not allowed. Cohort A included patients with radiotherapy-naive BM, and cohort B included those with progressive BM after whole brain radiotherapy or stereotactic conformal radiotherapy. The primary endpoint was confirmed central nervous system (CNS) objective response rate (ORR), as assessed according to the Response Evaluation Criteria In Solid Tumors version 1.1. Results: Between January 2018 and July 2020, a total of 78 female patients were included (Table). For cohort A (n = 59), the CNS ORR was 74.6% (95%CI: 61.6%-85.0%). For cohort B (n = 19), the CNS ORR was 42.1% (95%CI: 20.3%-66.5%). By the cutoff date on 25 January 2021, the median progression-free survival was 12.1 months (95%CI: 9.0-14.7) in cohort A and 5.6 months (95%CI: 3.4-10.7) in cohort B. The most common grade ≥3 adverse events were diarrhea (23.1% [18/78]), neutrophil count decreased (12.8% [10/78]), white blood cell count decreased (12.8% [10/78]), anemia (9.0% [7/78]), hand-foot syndrome (7.7% [6/78]), hypertriglyceridemia (6.4% [5/78]), and hypokalemia (5.1% [4/78]). Conclusions: Pyrotinib plus capecitabine resulted as an effective and safe treatment for HER2-positive BC patients with radiotherapy-naive BM, but the efficacy was modest in those with radiotherapy-treated BM. Clinical trial information: NCT03691051.