Abstract: Pear leaves were treated by different densities of nitric oxide donor—SNP after its infection with Pnysalosproa piricola Nose for five days and the activities of plasmalemma H⁺—ATPase and antioxidative enzyme were investageted. Results show that diseased pear treatment with SNP at the density of 0.3mmol/L can raise H⁺—ATPase, APX, GPX and GR activities and reduce LOX activity, while 0.1mmol/L and 0.6mmol/L SNP have less apparent effects on pear toxicity mitigation. In the treatment group of SNP at a constant density, there are varying degrees of effect on infected pear with the prolongation of treatment time. SNP in a relatively low density can palliate pear toxicity after Pnyalosproa piricola Nose infection.