A novel series of 2-styrylquinazolin-4(3H-ones which inhibited tubulin polymerization and the growth of L1210 murine leukemia cells was discovered. Extensive structure-activity relationship studies suggest that the entire quinazolinone structure was required, but activity was further enhanced by halide or small hydrophobic substituents at position 6. These analogues did not substantially interfere with the binding of radiolabeled colchicine, vinblastine, or GTP to tubulin and weakly stimulated GTP hydrolysis uncoupled from polymerization. Several analogues have shown in vivo tumor growth inhibitory activity in the L1210 leukemia model, with the lead compound 5o exhibiting good antitumor activity against murine solid tumors as well as human tumor xenografts.