Abstract: With the solution extracted from the roots zone soil of 6yearold Ailanthus altissima trees to treat the seed of Robinia pseudoacacia, the paper studied allelopathic effects of the extracts on seed germination and seedling growth of R.pseudoacacia. The results showed that inhibiting effects on the seed germination and young seedling growth were significant, which indicated that there should be some allelopathic chemicals in the root zone soil. The intensities of inhibiting effects for the extracts were different with treatments at different extraction concentration. Among the extractions, the effect of the 1.0 mg/mL treatment was the strongest. It was also concluded that the inhibiting effects for the extracts from the root zone soil of A.altissima on seed germination percentage and germination index were mild, while the effects on seed vigor index and root growth of the seedling were the strongest.