Fourty-three new benzoxazolinone derivatives having a piperazinomethyl group at the third position of the ring were synthesized by using appropriate benzoxazolinones and 4-substituted piperazines via a Mannich reaction. The structures of the compounds were elucidated by spectral data and microanalyses. Analgesic activities were evaluated by a modified Koster test. All compounds, except 7, 14, 21, 32 and 41, showed analgesic activity higher than that of acetylsalicylic acid. The compounds were also screened for their anti-inflammatory activity using a carrageenan paw edema test, and those exhibiting high anti-inflammatory activity were investigated for their ability to inhibit prostaglandin E2 induced paw edema. The results of anti-inflammatory testing indicated that most of the compounds were more active than indomethacin. Ulcerogenic activities of the compounds were also studied and no gastrointestinal bleeding was observed at the 100 mg/kg dose level.