Topoisomerase I inhibitor 4 (compound 7a) is a topoisomerase I inhibitor. Topoisomerase I inhibitor 4 inhibits HepG2, A549, MCF-7 and HeLa cancer cells proliferation with IC 50 s of 1.20, 2.09, 1.56 and 1.92 μM, respectively. Topoisomerase I inhibitor 4 can be used for the research of cancer.