A total of 6 newly-synthesized styrylchromones (SC-1 approximately SC-6) were compared for their cytotoxic activity against three normal oral human cells (gingival fibroblast HGF, pulp cell HPC, periodontal ligament fibroblast HPLF) and four human tumor cell lines (squamous cell carcinoma HSC-2, HSC-3, submandibular gland carcinoma HSG, promyelocytic leukemia HL-60). All compounds showed higher cytotoxic activity against tumor cell lines than against normal cells. Among the 6 compounds, SC-3, SC-4 and SC-5, which have one to three methoxy groups, showed higher tumor specificity and water solubility. The cytotoxic activity of SC-3 and SC-5 was slightly reduced by a lower concentration of NADH, a quinone reductase, but that of SC-3 was enhanced by higher concentrations of NADH, possibly due to demethylation of the methoxy groups. Agarose gel electrophoresis demonstrated that SC-3 and SC-5 induced intemucleosomal DNA fragmentation in HL-60 cells and production of large DNA fragment in HSC-2 cells. Both SC-3 and SC-5 enhanced the enzymatic activity to cleave the substrates for caspases 3, 8 and 9, suggesting the activation of both extrinsic and intrinsic apoptosis pathways. ESR spectroscopy showed that these compounds produced no detectable amount of radical and did not scavenge superoxide anion generated by the hypoxanthine-xanthine oxidase reaction. The highly tumor-specific cytotoxic action and apoptosis-inducing capability of SC-3 and SC-5 suggest their applicability for cancer chemotherapy.