Abstract: The bioassay results showed that Lophodermium conigenum, L. pinastri, L. sichuanense and L. erlangshanense fungi could produce pathotoxin that might have led to their host dying in the liquid medium. Study showed that the four mycotoxins were non-proteins components, and there were different toxicity between host needles and other several kinds of pine needles by combining with the determination of conductivity, especially the mycotoxin of L. sichuanense fungus had the strongest toxicity. The bioassay of three kinds of weeds from different family and Cedrus deodara showed that the four toxins were non-host specific.