Abstract: Pathogenic toxin of Leptographium yunnanense associated with Tomicus piniperda could pathogeny not only to Pinus yunnanensis,but also to P.armandii and P.kesiya var. langbianensis. The symptoms were very complicated and not easy to be observed and determined when bioassaying the toxin with seedlings cutted roots, however, when bioassaying the toxin with sampling trees and its wood blocks, the symptoms would be observed clearly, and as the same as they were induced by inoculating the fungus to the host trees. The bioassay results would be observed sooner (about 5 days) when bioassaying the toxin with wood block, so it was better to inoculate the pathogenic toxin to the wood blocks for bioassay.