Abstract: The allelopathic effects of leaf litter (in the initial decomposition process of litter in soil) of Eucalyptus grandis on growth and resistance physiology of Elymus sibiricus was studied in a pot experiment. Each pot contained 8 kg soil mixed with 0, 25, 50, 100, or 150 g leaf litter. E. sibiricus was sown in September and height, biomass and several indices of resistance physiology were tested at 30, 40, 50, and 90 d after sowing. 1) Height and biomass of E. sibiricus were significantly inhibited after 90 d. 2) The activities of SOD and CAT in leaves of E. sibiricus increased in conditions of low litter content and short decomposition times but were inhibited with higher-contents of litter or longer treatment times. POD was significantly inhibited by different treatments after 90 days. 3) The MDA content rose with the increasing litter content at 50 d, but had decreased in all treatments by 90 d. 4) The soluble carbohydrate content increased considerably, whereas that of soluble protein had considerably reduced by 90 d. 5) The effects of leaf litter decomposition in soil was high at first but then weakened. Faster and stronger allelopathic effects were observed in treatments with higher litter content than those with lower ones. The compound effect of the 150 g treatment was the strongest, while that of 50-100 g treatments were weaker, and the 25 g treatment was the weakest. On the whole, the leaf litter of E. grandis had a strong allelopathic effect on E. sibiricus in the initial decomposition process of litter in soil.