Chronic myelogenous leukemia (CML) is clinically treated with imatinib, which inhibits the kinase activity of the Bcr-Abl oncoprotein. However, imatinib resistance remains a common clinical issue. Andrographolide, the major compound of the medicinal plant Andrographis paniculata, was reported to exhibit anticancer activity. In this study, we explored the therapeutic potential of andrographolide and its derivative, NCTU-322, against both imatinib-sensitive and imatinib-resistant human CML cell lines. Both andrographolide and NCTU-322 downregulated the Bcr-Abl oncoprotein in imatinib-resistant CML cells through an Hsp90-dependent mechanism similar to that observed in imatinib-sensitive CML cells. In addition, NCTU-322 had stronger effects than andrographolide on downregulation of Bcr-Abl oncoprotein, induction of Hsp90 cleavage and cytotoxicity of CML cells. Notably, andrographolide and NCTU-322 could induce differentiation, mitotic arrest and apoptosis of both imatinib-sensitive and imatinib-resistant CML cells. Finally, the anticancer activity of NCTU-322 against imatinib-resistant CML cells was demonstrated in vivo. In summary, our data demonstrated that andrographolide and NCTU-322 inhibit Bcr-abl function via a mechanism different from that of imatinib, and they induced multiple anticancer effects in both imatinib-sensitive and resistant CML cells. Our findings demonstrate that andrographolide and NCTU-322 are potential therapeutic agents again CML.