Abstract: 【Objective】 To improve the biological control efficiency of fruit tree canker in Karamay.【Method】The diseased and soil samples were collected from the infected plants of apple tree and plum tree rot disease of Populus Karamayi. The pathogenic bacteria and their antagonistic bacteria were screened. Additionally, the molecular identification of microorganism and the analysis of antagonistic effect were carried out.【Result】The research showed that the pathogen of apple tree and plum tree rot was both of the genus Valsaa, in which the pathogen of plum tree is related to two species of this genus: Valsa mali and Valsa leucostoma; Valsa mali and Valsa leucostoma led to the plum tree canker, Valsa mali led to the apple tree canker, respectively. 15 antagonistic isolates against the fungi were screened and classified in 9 species of 4 genera. Particularly, 2 strains displayed high antagonistic activity. The maximum colony inhibition ratio was 2.11 and 2.79, respectively, and microscopic characteristics of the edge mycelia of Valsa Mali around inhibition zone by B6 and B4 indicated that there were significant differences between the two strains in killing fungi.【Conclusion】The pathogen of plum tree canker was reported for the first time. Meanwhile, it provided the basis and material for efficient biological control to fruit trees canker.