Abstract: Phenolic allelochemicals such as vanillic acid, syringic acid, ferulic acid and p-coumaric acid, have been proved to be autotoxins produced by Panax quiquefolium.L. In order to elucidate the interaction between the autotoxins and the disease occurence in ginseng fields, we investgated the effects of the four phenolic acids on the mycilum growth of two pathogens isolated from ginseng and the fields. The mycelial growth of Rhizoctonia solani was promoted by vanillic acid and syringic acid at levels of 0.1~1 mM/L, and it was inhibited remarkably by p-counaric acid of over 1mM/L and modestly by ferulic acid. The radial extent of mycelia of Fusarium solani was increased significantly by ferulic acid of 0.1~1 mM/L and limitedly by p-coumaric acid. vanillic acid had paradoxcial effects on the growth, positively at low levels and negtively at high levels, on which Syringic acid had a slight effect. It is concluded that various phenolic acids had irregular effects on the growth of the pathogens at different concentrations, and there is a complicated relationship between the autotoxins and the occurrence of disease in the ginseng field.