[ Objective] This study was to investigate the pathogenic mechanism of rice sheath blight pathogen （ Rhizoctonia solani） and the bioactive components of toxin. [ Method ] Rice sheath blight pathogen was cultured in the improved Richared medium; the culture filtrate was centrifuged and sterilized, then treated by activated carbon adsorption chromatography, distilled with methanol or water, and all were next concentrated, yielding the crude extracts of culture solution, crude extracts of methanol and crude extracts of water; the activities of these three extracts were determined, [ Result] The three extracts were russet pastes; activity determination showed that they had remarkable inhibitory effects on the growth of rice radicle and plantule, as well as the growth of four-foliage-young seedlings. They could also generate toxic effects on abscisic foliages and spots similar to the symptoms of sheath blight pathogen. [ Conclusion] Bioactive components of rice sheath blight pathogen toxin may be composed of various ingredients.
