Background: Pyrotinib, an irreversible pan-ErbB receptor tyrosine kinase inhibitor, showed promising anti-tumour activity and acceptable tolerability in patients with HER2+ metastatic breast cancer (MBC) in phase 1/2 trials. Methods: This double-blinded, multicentre, randomised phase 3 trial was conducted in Chinese patients with HER2+ MBC previously treated with taxanes and trastuzumab. Patients were randomly assigned (2:1) to receive 400 mg pyrotinib or placebo orally once daily for 21-day cycles in combination with capecitabine (1000 mg/m² orally twice daily on days 1–14). The primary endpoint (IRC-assessed progression free survival [PFS]) was assessed in patients who received ≥1 dose of study treatment. Patients whose disease progressed on placebo plus capecitabine received subsequent single agent pyrotinib. Results: Between July, 2016 and November, 2017, 279 patients were randomised to pyrotinib plus capecitabine (n = 185) or placebo plus capecitabine (n = 94) arms. The median PFS was 11.1 months (95% CI 9.66, 16.53) in the pyrotinib plus capecitabine arm and 4.1 months (95% CI 2.79, 4.17) in the placebo plus capecitabine arm. seventy-one patients in placebo plus capecitabine arm received subsequent pyrotinib, showing single-agent response rate of 38.0% (95%CI 26.7%, 49.3%) and median PFS of 5.5 months (95% CI 4.07, 6.90). The most frequent (≥5%) treatment-related ≥ grade 3 adverse events were diarrhoea (30.8% vs 12.8% ) and hand-foot syndrome (15.7% vs 5.3%). Conclusions: In women with HER2+ MBC previously treated with taxanes and trastuzumab, pyrotinib plus capecitabine yield statistically significant better PFS. Pyrotinib monotherapy showed anti-tumour activity. Clinical trial information: NCT02973737