Abstract: Objective : To investigate the effects of Huaier extract on B lymphocytes and their subsets in patients with immune thrombocytopenia purpura (ITP). Methods: The peripheral blood of 20 patients with ITP diagnosed in The Second Affiliated Hospital of Dalian Medical University from January 2019 to March 2020 were analyzed. The median age was 53.5 (16.0 - 87.0) years, including 8 males and 12 females. CD19⁺B-lymphocytes and their subsets, CD19⁺CD27⁺ memory B and CD19⁺CD24⁺CD38⁺ regulatory B cells, were compared between patients with ITP and normal controls using flow cytometry. Next, cells from a B-lymphocyte line were treated with different concentrations (2, 4 ,6 mg•mL^-1) of Huaier extract. CCK-8 was used to assess the effect of Huaier extract on B-lymphocyte proliferation. Changes in B-lymphocyte subsets in peripheral blood treated with Huaier extract for 72 h were determined using flow cytometry. Results: The proportion of CD19⁺B-lymphocytes was significantly higher in patients with ITP than in normal controls. Huaier extract can inhibit the proliferation of B-lymphocytes, as well as the proliferation of regulatory B cells and memory B cells in patients with ITP. Conclusions: Huaier extract can inhibit the proliferation of B-lymphocytes in patients with ITP, providing a possible theoretical basis for clinical application.