The low-molecular-weight antibiotic substances of low molecular weight induced in rice leaves by salicylic acid(SA) treatment were studied. Plate method was used to detect the effect of the extract on spore germination and Gas chromatography-mass spectrometry(GC-MS) was used to analyse these low-molecular-weight antibiotic substances. The results showed that the induced substances can effectively inhibit spore germination in Magnaporthe grisea.GC-MS analysis also revealed that SA could significantly induce many kinds of low-molecular-weight compounds in rice leaves and that their content was increased as compared to the control group. SA could cause the production of momilactone A, momilactone B, eugenol, and chorismic acid evidently，SA could alter the levels of phenol, methyl salicylate, stigmasterol, β-sitosterol, undecane and methyl ester. These results provided direct evidence that the rice plant produces phytoalexins in response to SA treatment.