Certain activator was expected to be developed to improve the free radical intermediates relative intensity,and thus to enhance the adhesion between wood fibers when fiberboard was made by laccase treated wood fibers.Reactive oxygen species(ROS)was detected in laccase-catalyzed oxidation of wood powder using ESR spin trapping technique.The effects of five metal ions(Cu2+,K+,Fe2+,Mg2,Fe3+)and EDTA on ROS relative strengths were investigated under the condition of pH 5.6 by electron spin resonance spectrometry.The result shows that Cu2+ slightly activates the free radical reaction,and Fe2+ ion has a significant inhibitive effect on the ROS relative strength in the suspension liquid.There is a marked inhibition of the ROS relative intensity when 0.5 mmol/L EDTA is used.The metal ions that enhance laccase activity may be utilized to increase physical properties of fiberboard made by laccase oxidized wood fibers.