[Objective] Acute toxicity of fresh leaves of Populus nigra to mice were studied to evaluate the biological safety.[Method]Taking transgenic Populus nigra and non-transgenic Populus nigra as test substance,unintended effects of insect-resistant transgenic Populus nigra was studied. [Result] There was not any death of mice after treating for 7 days,and no obvious acute effect in general condition and general dissecting. The half lethal dose( LD50) was greater than 10. 0 g/kg·bw,result showed that it was clas...