Zanubrutinib is a selective second-generation Bruton tyrosine kinase inhibitor approved in various B-cell malignancies globally. The phase 1/2 BGB-3111-111 study evaluated the efficacy and safety of zanubrutinib 160 mg twice daily orally in Japanese patients with treatment-naive or relapsed/refractory mature B-cell malignancies. Here, efficacy results from Part 2 in chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL; n = 19) and Waldenström macroglobulinemia (WM; n = 19), and safety results from Parts 1 (N = 6) and 2 (N = 49) are presented, with the first dose between 30 January, 2020, and 31 October, 2022. As of 10 May, 2023, investigator-assessed overall response rates were 100% (19/19) and 94.7% (18/19) in CLL/SLL and WM, respectively, with median follow-up of 27.9 and 26.8 months; 24-month progression-free survival rates were 71.4% and 100% in treatment-naive and relapsed/refractory CLL/SLL and 83.9% and 100% in treatment-naive and relapsed/refractory WM, respectively. In patients with B-cell malignancies, any-grade treatment-emergent adverse events (TEAEs) occurred in 53 (96.4%) and serious TEAEs in 18 (32.7%). Common TEAEs were platelet count decreased (18.2%), pyrexia (18.2%), COVID-19 (14.5%), and neutrophil count decreased (12.7%). With median follow-up > 2 years, zanubrutinib demonstrated durable efficacy in Japanese patients with CLL/SLL or WM and a favorable safety profile consistent with global phase 3 studies.