Abstract:Bursaphelenchus xylophilus and B. mucronatus were further confirmed to be two different species. The pathogenicity and the bursa forms of the twospecies evidently differ from each other, the bursa of the former species iseggshaped, while that of the latter species is flatmouthshaped. The physiological tests indicated that the two species couldn‘t mate with each other.Biochemical experiments showed that the former species esterase had three isoenzyme bands, and its relative electrophoretic mobilities (Rf) were 0. 42, 0. 45and 0.49 respectively, and that the latter species‘esterase only had oneisoenzyme band and the Rf was 0.65. On the other hand, there were obviousdifferences between the two species about the distribution of fatty acids.