Some novel 3-phenyl-2-[(E)-2-phenylethenyl]-3,4-dihydroquinazolin-4-one derivatives possessing para-sulfonamides groups on the phenyl ring of the 2-phenylethenyl moiety have been synthesized and their COX-2 inhibitory activity evaluated. The stuctures of the synthesized compounds were confirmed on the basis of FT-IR, 1H-NMR, 13C-NMR and mass spectral data. The COX-2 inhibition screening assay revealed that 4-[(E)-2-{3-(4-methoxyphenyl)-4-oxo-3,4-dihydroquinazolin-2-yl}ethenyl]benzene-1-sulfonamide had a maximum COX-2 inhibition (47.1%), at a concentration of 20 μM.