In this study, we have explored the prevention of gastric side effects such as gastric lesions and bleeding while maintaining the high analgesic and anti-inflammatory activities by the derivatization of the carboxylate moiety into amides in [5-chloro-6-(2chloro/fluorobenzoyl)-2-benzoxazolinone-3-yl]acetic acids. We have tested the analgesic and anti-inflammatory activities of the synthesized compounds in vivo by using p-benzoquinone-induced writhing test and carrageenan-induced hind paw edema model, respectively Compounds 3a, 3d, 3e, 3j and 3k showed potent analgesic and anti-inflammatory activities without gastric lesions in the tested animals. Therefore, conversion of the carboxylate moiety into certain amide derivatives generated potent analgesic and anti-inflammatory compounds while eliminating the gastrointestinal side effects. Cyclooxygenase (COX)-selectivity of the active compounds was also investigated by using in vitro human whole blood assay. Compounds 3 a, 3 e, 3 h and 3 k demonstrated selective inhibition of COX-2 to some extent although the inhibitory activity was not very potent.