A new series of 2-aryl, 3-benzyl-(1,3-oxazolidine or 1,3-thiazolidine)-4 ones, possessing a methylsulfonyl pharmacophore, were synthesized to evaluate their biological activities as selective cyclooxygenase-2 (COX-2) inhibitors. In vitro COX-1 and COX-2 isozyme inhibition studies were performed to acquire structureactivity relationship data with respect to the point that molecular modeling studies showed that designed compounds bind in the primary binding site such that the C-2 para-SO2Me substituent inserts into the 2 pocket present in COX-2 enzyme. COX-1 and COX-2 inhibition studies showed that all compounds were selective inhibitors of the COX-2 isozyme with IC50 values in the highly potent 0.21 to 0.34 lM range, and COX-2 selectivity indexes in the 222.3 to [476 range. 3-Benzyl-2-(4-methylsulfonylphenyl)-1,3-oxazolidine-4(5H)-one was identified as the most potent (IC50 = 0.21 lM) and selective (S.I.[476) COX-2 inhibitor among the synthesized compounds. It also was a more selective COX-2 inhibitor than the parent reference compound celecoxib (S.I. [403).