Sixteen (2-benzothiazolone-3-yl and 2-benzoxazolone-3-yl) acetic acid derivatives 5 have been tested for anti-nociceptive and anti-inflammatory activity in this study, 4-[2-(6-Benzoyl-2-benzoxazolone-3-yl)acetyl]morpholine (5c), 4-¿2-[6-(2-chloro-benzoyl)-2-benzoxazolone-3-yl]acetyl¿morpholine (5d), 1-[2-(5-chloro-2-benzoxazolone-3-yl)acetyl]pyrrolidine (5f), methyl (6-methyl-2-benzoxazolone-3-yl)acetate (5k) and N,N-diethyl-2-(2-benzothiazolone-3-yl)acetamide (5m) have shown more potent anti-nociceptive activity than others. Among these compounds, 5c, 5d and 5m have exhibited good anti-inflammatory activity, with 5f, and to a lesser extent, the other molecules displaying some toxic potential.