Phenolic compounds, p-coumaric and p-hydroxybenzoic acids, known as inhibitors for development and growth of many pioneer species on early stage of succession were used for the test of susceptibility in various herbs collected from abandoned agricultural fields in the vicinity of Amherst(U.S.A). The percent inhibition was generally greater for p-coumaric acid than for p-hydroxybenzoic acid. Concentrations of 5×10 exp(-5) and 5×10 exp(-4) M generally had no significant effects, but at 5×10 exp(-3) M was inhibitory to germination and growth of tested species. And the percent inhibition caused by the two phenolics was correlated(r=.843, p<.01). Also the indices of resistance for germination and clongation were significant(r=.695, p<.01) in this study. While Cirsium and Lepidium invading species of early stage of succession were sharply susceptible for toxic activity by phenolic acids.