In this paper, the extraction and bioactivity assay of pathotoxin produced by Phytophthora sojae (Pmg.) were systematically researched. The main results were as follows: The best extraction way of the pathotoxin produced by Pmg was to use the weak polarity organic solvent, especially ether. The rude crystalline of the pathotoxin was gotten by continuous extraction by ether; The bio-activity of the rude pathotoxin was determined by the seedlings with cutting roots, and the symptom of seedlings with cutting roots treated with the concentration of the dilute factor of 100 appeared the same as those with the hypocotyl inoculation. This also proved that the pathotoxin was a kind of Non- Host Specitiy Toxin.