The synthesis of a novel series of Mannich bases of 5-/6-acyl-5-methyl-2-benzoxazolinones has been described. The structures attributed to compounds 2a, 3a, 4a, 4b, 9a, 9b, 5a-5g, 6a-6g, 10a, 10g, 11a, 11g have been elucidated using IR and (1)H NMR spectroscopic techniques besides elemental analysis. The compounds have been evaluated for their in vivo analgesic and antiinflammatory activities using the p-benzoquinone-induced writhing test and the carrageenan hind paw oedema test 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 a 6-(4-chlorobenzoyl) at C-6 position and 2-/4-fluorophenyl at C-3 position of 2-benzoxazolinone ring (11c, 11d).