The anti-inflammatory activities of several novel oximes and O-acyl oximes that we synthesized have been reported based on carrageenan-induced rat foot-pad swelling assay and histamine-induced rat vascular permeability assay. A cyclooxygenase (COX)-1 inhibitory effect has also been reported for 4′-piperidinoacetophenone and 4′-morpholinoacetophenone oximes and their O-acyl derivatives. To further search for more effective non-steroidal anti-inflammatory or anti-allergic drugs, 1-hydroxylamino-1-(4′-piperidinophenyl) ethane (P-HA) and 1-hydroxylamino-1-(4′-morpholinophenyl) ethane (M-HA) were synthesized from the corresponding oximes with sodium cyanoborohydride, and N,O-diacetyl hydroxylamines (P-HA-Ac and M-HA-Ac) were prepared from these hydroxylamines using acetyl chloride. These hydroxylamines and N,O-diacetyl hydroxylamines clearly exhibited inhibitory effects on mouse carrageenan-induced foot-pad swelling induced by oral administration (150, 37.5 mg/kg). An oral dose of P-HA-Ac (150 mg/kg) significantly inhibited the mouse anaphylactic reaction to ovalbumin measured by the abdominal wall (AW) method. Percutaneous administration of P-HA and M-HA significantly inhibited 2,4-dinitrofluorobenzene (DNFB)-induced contact hypersensitivity reaction (type IV) in mice at a dose of 0.5 and 0.1 mg/ear, respectively. All tested hydroxylamines and N,O-diacetyl hydroxylamines clearly inhibited both COX-1 and COX-2 enzyme activities with IC₅₀ values of 1.9—28.7 and 1.6—2.9 μM against COX-1 and COX-2, respectively. Hydroxylamines (P-HA and M-HA) also showed a 5-lipoxygenase inhibitory effect.