By taking the methods of indoo r dish cul ture test, po t cul ture ex periment in g reenhouse, and experiment of field plo t , the inhibi ting effect of chitosan on so ybean roo t rotpathog ens: Fusarium , py thium, rhizoctonia, phytophthora w as determined. The biocontro l ef fect of Chitosa n on soy bean roo t ro t w as appraised. The resul t show ed: Chitosanhad defini te inhibi ting ef fect o n soy bean root ro t in PDA dish culture. In Chi to sansoybean seed t reatment the disease incidence and index of di sease of soybea n roo t rotdropped obviously , the cont rol effect w as42. 6- 46. 9% . At the same time, Chi to sancould promote g row th of soy bean root ro t plant g row th mo re healthy a nd No. of po dsper plant , No. o f seeds per plant, seed weight increased, soybean yield increased 11.7% .