In this study, the synthesis of a novel series Mannich bases of 5-nitro-3-substituted piperazino-methyl-2-benzoxazolinones are described. The structures attributed to compounds 3a-3k were elucidated using IR, H-1-NMR spectroscopic techniques besides elemental analysis. The compounds were examined for their in vivo anti inflammatory and analgesic activities in two 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 tested derivatives most promising results were obtained for the compounds bearing electron-withdrawing substituents (F, Cl, COCH3) in the ortho/para position of the phenyl nucleus on the piperazine ring at 3 position of benzoxazolinone moiety (3a, 3b, 3c, 3d, 3h). The analgesic activities of all compounds are higher than their anti inflammatory activities. Antiinflammatory inhibitory ratios for all compounds were above 30% for the last two measurements. Because of this compounds 3a, 3b, 3c, 3d deserve attention and may be considered for further evaluation.