Abstract: Inhibiting effects of some 4-subftitutcd 2,2,6,6-tctramethylpiperidine derivatives incorporated with quinone on MMA,initiated by benzoylperoxide,have been investigated by boiling,refractive index and electron spin resonance methods respectively.The result showed that when 2,2,6,6-tetramethyl-4-oxo-piperidine-i-oxyl(I),2,2,6,6-tetramethyl-4-oxime-piperidine-i-oxyl(Ⅱ),2,2,6,6-teiramethyl-4-hydrooxy-piperidine-i-oxyl(Ⅲ)was incorporated with 1,4-benzoquinone,chlor-anil,1,4-naphthoquinonc or 9,10-phenonthrenequinone,inhibiting effects of these complexes would become more prominent than when nitroxyl radical was used alone.Especially incorporative effect of nitroxyl radical with l,4-benzoquinone was much more satisfying than that of other quinone.The control test also showed that it was not active for 1,4-bihydrooxy-2,2,6 ,6-tctramethylpiperidine(Ⅳ),1-(2-cyano-2-propyloxy)-4-oxo-2,2,6,6-tetramethylpiperidine(Ⅴ)and 1-phenoxy-4-hydroxy-2,2,6,6-tetramethyl-piperidine(Ⅵ)to inhibit polymerization of MMAat 101℃ when it was used alone,but it was so satisfactory inhibitor of MMAas parent ni-troxyl radical when they were incorporated with quinone.The inhibition mechanism was studied by ESR spectral measurement.These research result demonstrated that the inhibiting mechanism of nitroxyl radical in the polymerization of MMAwas proposed to have couple and abstraction.hydrogen reaction and so on.