Abstract: Salicylic acid(SA)was applied on Taizishen(Pseudostellaria heterophylla)to induce the plant's resistance to the leaf spot disease.Enzyme activities relating to the disease-resistance were investigated.In vitro-regenerated Taizishen plantlets were treated under aseptic conditions with 6 different concentrations of SA,0.5-15 mmol-1,to determine the optimum SA induction level.Activities of various enzymes in the leaves were determined within 1-7 days after SA treatment.The disease-resistance of the treated plantlets was observed with the application of a water suspension of the leaf spot spores,7 days after the treatment.The results showed that(a)the activity of the enzymes,such as peroxidase and polyphenol oxidase,in the leaves was enhanced by SA treatment;(b)the catalase activity was significantly inhibited after induction by SA at a concentration of 5 mmol-1;and(c)POD activity increased by 170%,PPO increased by 293%,and CAT decreased by 43.3%,as compared to the control.SA concentration in the range of 0.5-15 mmol-1 appeared to be capable of inducing the disease-resistance in Taizishen.The best result seemed to be at the concentration of 5 mmol-1 SA,as the average effective rate was 59.6%,which was significantly higher than those achieved by the other treatments.