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, $^1$H-NMR spectroscopic techniques besides elemental analysis. The compounds were examined for their in vivo antiinflammatory and analgesic activities in two different bioassays, namely, carrageenan-induced hind paw edema and p-benzoquinone-inducedabdominal 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, COCH$_3$) in the ortho/para position of the phenyl nucleus on the piperazine ring at 3 position of benzoxazoli-none moiety (3a, 3b, 3c, 3d, 3h). The analgesic activities of all compounds are higher than their antiinflammatory 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.