Romiplostim is approved for the treatment of immune thrombocytopenia (ITP). This study aimed to evaluate the pharmacokinetics, safety, and pharmacodynamics of romiplostim in Chinese patients with ITP. This multicenter, open-label, dose-escalation phase I/II trial enrolled ITP patients from 5 centers in China between October 2015 and August 2017. There were 2 cohorts: 1 μg/kg and 3 μg/kg weekly for 2 weeks. The end points included pharmacokinetics, platelet changes from baseline, hematological indicators, and adverse events (AEs). Sixteen participants, with 8 patients in each cohort, were enrolled. In the 1 μg/kg cohort, time to maximum concentration was 4.00 (4.00-7.83) hours, maximum serum drug concentration was 52.0 (16.0-228.0) pg/mL, and area under the serum drug concentration-time curve from time 0 to the last detectable time point was 389 (32.0-5400) pg · h/mL. In the 3 μg/kg cohort, time to maximum serum drug concentration was 11.91 (4.00-12.00) hours, maximum serum drug concentration was 105.0 (25.5-313.0) pg/mL, and half-life was 12.7 (8.2-23.6) hours. The absolute change of peak platelet count from baseline was 14 (3-40) and 72 (3-369) ×109 /L in the 1 and 3 μg/kg cohorts, respectively. Seven (87.5%) and eight (100%) participants had treatment-emergent AEs in 1 μg/kg cohort and 3 μg/kg cohort, respectively. No major AEs occurred in the 2 cohorts. Romiplostim (1 and 3 μg/kg) is safe and well tolerated in Chinese patients with ITP.© 2021 The Authors. Clinical Pharmacology in Drug Development published by Wiley Periodicals LLC on behalf of American College of Clinical Pharmacology.