Abstract: By using pot experiments,researches was conducted on the effects of leaf litter of Populous on the growth and resistance physiology of Lactuca sativa during the decomposition process of leaf litter. Each pot contained 8 kg soil mixed with 30,60,90 and 0 g leaf litter. Height,biomass,and several resistance physiology indexes of Lactuca sativa were determined on 50 d after sowing. The results showed that 1) the heigh of A₃ was inhibited significantly on 50 d after planting,and the biomass of A₂ and A₃ was inhibited significantly; 2) The activities of superoxide dismutase (SOD) increased in low litter content and decreased in higher litter content; 3) The content of malondialdehyde (MDA) of A₂ and A₃ was higher than that of control(CK),and moreover,it increased along with the addition of leaves; 4) The content of soluble sugar(SS) in each treatment was significantly higher than that of control(CK),whereas the content of soluble protein (SP) was significantly lower than that of control(CK). On the whole,the high content leaf litter of Populous had a serious allelopathic effect on Lactuca sativa during its initial decomposition process in soil.