Abstract: Transmission. electron microscopical observations on the effects of pyquiton on po-gumogonimus skrjabini in dogs were carried out. 24 hours after oral administration of single dose of 120mg/kg pyquiton to dogs infected with Pagumogonimus skrjabini, the tegumental cytoplasmic projections swelled, the mitochondria in the ground substance; were concentrated, the secretory bodies decreased, the nucleolus and chromatin in the tegumental cells and the musculature were dissolved and the muscular microfilaments were disordered. Simultaneously, the nucleus and nucleolus of the gut epithelia were swollen, the chromatin concentrated, the secretory body disappeared and the microvilli on the surface of digestive tract adhered together and ruptured. Finally, the mechanism of pyquiton in killing Paragonimus was discussed on the basis of the findings in this study (Plates 1-8).