In an effort to develop potent anti-cancer chemopreventive agents that act on topoisomerase II, a novel series of bisindolylalkanes analogues such as 3,3'-(thiochroman-4,4-diyl)bis(1H-indole) are synthesized. Structures of all compounds are elucidated by (1)H NMR, (13)C NMR and HRMS. Anti-proliferative activities for all of these compounds are investigated by the method of MTT assay on 7 human cancer lines. Most of them showed antitumor activities in vitro, the half maximal inhibitory concentration (IC50) value is 7.798 μg/mL of 3a against MCF7. Compound 3a showed comparable topoisomerase II inhibitory activity to etoposide (VP-16) at 100 μM concentration. The rest of the compounds also showed varying degree topoisomerase II inhibitory activity.