Meisoindigo ((E)-1,1'-dimethyl-[3,3'-biindolinylidene]-2,2'-dione) is a derivative of Indigo Naturalis, that has been used in China for chronic myeloid leukemia. In vitro cell line studies have shown that this agent might induce apoptosis and myeloid differentiation of acute myeloid leukemia (AML). Meisoindigo has been a routine therapeutic agent in the clinical treatment of chronic myelogenous leukemia (CML) in China since the 1980s. In phase III clinical trial of Meisoindigo involving 402 patients, it was shown that Meisoindigo was equally efficient for both newly diagnosed and previously treated CML patients after oral administration. The hematological complete response (CR) and partial response (PR) rates, respectively, were 45.0 and 39.3% for newly diagnosed patients and 35.9 and 41.4% for previously treated patients. Meisoindigo was generally well tolerated. The most frequent side‑effects were bone, joint and/or muscle pain of varying degrees when the dosage was more than the suitable one.