The genetic relationship of 16 isolates of Bursaphelenchus xylophilus and B. rnucronatus from Japan, South Korea, United States, Canada and China was examined using 10 primers by random amplifild polymorphic DNA(RAPD). The. dendrogram generated from the analyses revealed a significant difference between B. xylophilus and B. mucronatus, and among the isolates of B. xylophilus, three sub-groups w. ere divided (1) Chinese and Japanese isolates, (2)Taiwan China and American isolates, (3)Canadian isolate. The isolates of B. rnucronatus also could be divided into 2 sub-groups, (1)Japanese, Taiwan China and Jiangsu China isolates, (2)South Korea and Hunan China isolates.