Abstract: A number of bacteria had been isolated from different parts of poplar in Liaoning,Heilongjiang Province and Beijing City. About 60% of the bacteria strains showed ice nucleaticn activity under.5～6℃.Among them,the majority of the bacteria were isolated from the frozen bark of the poplars and most of them were INA bacteria,which could also be isolated from large canker lesions caused by Dotheorella gregaria Sacc.The overwintered one-year-old poplars were inoculated separately by Pseudomonas syringae isolated from the leaf or Erwinia herbicola isolated from large canker lesion. The freezing temperature of stems was tested under laboratorial simulation conditions. The stems inoculated by both of the INA bacteria suffered frost injury at -1.7℃ and -2.2℃ respectively,whereas the frozen state of the checks appeared at -4.6℃.The results showed that, INA bacteria were distributed widely in nprthern poplars. In the courses of frost injury,those INA bacteria exerted important effect on the formation of frozen barks.Probably they also have some influrences in the formation of large canker leslons.