Abstract: This study aimed to determine the relationship between allelopathy and soil microorganisms in order to find out the possible barriers that inhibit continuous cropping of soybeans.By altering two organic acids(i.e.,malic and tartaric acid)and three phenolic acids(i.e.,oleic acid methyl ester,2,4-dinitrophenol and vanillic acid)among the known soybean root exudates,the effect on the biomass and activity of the microbes in soil was determined.Using the soil sample collected from the continuous cropping field in Heilongjiang province,the in-lab frankia culture method was employed and the carbon/nitrogen ratio of the soil microbial biomass measured to preliminary identify the major components in the exudate.The results indicated that the addition of malic acid,tartaric acid and oleic acid methyl ester benefitted the microbial growth without allelopathy effect.On the other hand,the addition of2,4-dinitrophenol and vanillic acid at low concentrations increased the microbial biomass,while reduced it at high concentrations.The results suggested that 2,4-dinitrophenol and vanillic acid might play an important role in the soybean allelopathy.