Abstract: T he scavenging activities for and of 4-oxy-and-4-hydroxy-Nitrox ides and its derivatives(4-TEMPO) were studies. Superox ide anions()generated in a phenazin methosulphate(PMS)-NADH systtem were assayed by the reduction of mitroblue tetrazolium(N BT)Hydroxy radicals generated in“Fen ton reaction" were detected by spin-trapp ing technique NitroxIide free rad icals HTM PO、0TM PO and I-hydroxy I com pounds HTM POH、OTMPOH can scavenging during the cconcenentrations of 4-EMPO are 40-160μmol×L^-1 The effect is clearly different from the control group(P< 0.05or p<0.01)^. HTMP、HTMPO and 1-hydrox-yl compounds can treduce the signal of DMPO-OH^. during their concentrations are 16-160 mol×L^-1, but the signal of DMPO-OH^. ie raise HTMP and OTM P have no effect for OH^. and whichindicated that them echnnism of scavenging may be related to the stopping radical-chain reation directly or analogy with superoxide dismutase(SOD). It is necessary that the mechanisms of effect for or DMPO of 4-TEMPO were studied further.