Abstract:Four transgenic Populus nigra plants which were transformed with Bacillus thuringiensis toxin gene and showed high insect resistance were analysed by Western blot method. The result showed that 55kD polypeptides were found in the positive control and four transgenic plants showed Bt. Toxin gene was not only inserted into the chromosomes of poplar, but also expressed into protein. The result gave a direct evidence to explain the four plants‘s high insect resistance.