Abstract: Marine dinoflagellate Protoceratium reticulatum producing yessotoxins was mass cultured. Then obtained algal cells were extracted by ultrasonic crushing with methanol for yessotoxins. Macroporous adsorption resin (HP20) was used to adsorb the extracellular toxin secreted in the culture medium, and the yessotoxins adsorbed on the resin were eluted with 70% ethanol. Nine of yessotoxin and their analogues were detected by high performance liquid chromatography-tandem mass spectrometry in extracts. The toxin of yessotoxin accounted for 95.1% of the total toxin group in the extracts, derivative 41YTX accounted for 3.65%, and other trace analogues accounted for 1.25%. Yessotoxin was purified through high performance preparation liquid chromatography for 5 times. The molecular weight and molecular formula was confirmed as 1142.4747 and C₅₅H₈₂O₂₁S₂, respectively, by high resolution mass spectrometry. The purity of yessotoxin detected by quantitative nuclear magnetic method was more than 99%, meeting the requirement for preparation of yessotoxin standard material.