The synthesis of a novel series of Mannich bases of 5-methyl-3-substituted piperazinomethyl-2benzoxazolinones is described. The structures attributed to compounds 3c, 3d and 3f-3n were elucidated using IR and H-1 NMR spectroscopic techniques as well as elemental analysis. The compounds were examined for their in vivo anti-inflammatory and analgesic activities in 2 different bioassays, namely, carrageenan-induced hind paw edema and p-benzoquinone-induced abdominal constriction tests in mice, respectively. In addition, the ulcerogenic effects of the compounds were determined. Among the derivatives tested the most promising results were obtained for the compounds bearing electron-withdrawing substituents (F, Cl, COCH3) in the para position of the phenyl nucleus on the piperazine ring at the 3 position of benzoxazolinone moiety (3a, 3c, 3i). The analgesic activities of all compounds are higher than their anti-inflammatory activities and therefore these high analgesic activities indicated that the compounds could a show central effect.