Albendazole is a broad spectrum anthelmintics with high activity against intestinal nematodes as well as tremtodes and cestodes infections. But so far wormicidal effect of albendazole against Paragonimus westermani is uncertain. The present study undertaken to observe the morphological changes of Paragonimus westermani which was obtained from experimentally infected with metacercariae isolated from Cambaroides similis and 9 of them were given albendazole 2 doses of 25mg/kg daily for the 2 days and 4 days from the day of 20 weeks after infection. The Paragonimus werms were collected from the lung of the cats which were autopsied at 24 hours after treatment. The fine structures of the collected worms were studied by means of scanning and transmission electron microscopy. The findings of the observations were compared with those of untreated worms. The results are as follows : 1) In the scanning electron microscopic(SEM) observations, the worms obtained from 2 days treated group showed many blebs which were formed on the surface of damaged tegument in between two suckers. Protrusion of oral sucker typically observed and surrounding tegumental ridges were damaged. 2) The worms obtained from 4 days treated group showed marked contraction revealing half size of normal worms. 3) The transmission electronmicroscopic(TEM) observations indicated that large blebs of irregular shapes were formed by the destruction of tegumental ridge of tegumental syncytium and also showed degeneration of mitochondriae. 4) Destruction of tegumental syncytium formation of blebs were usually observed in the ventral side of the worms. 5) Differentiation of tegumental layer and basement layer muscular layer and parenchymal layer around two suckers of worms obtained at 4 days treated group was difficult. 6) Many host cells invaded and destroyed the degenerated tegument by the occurrence of blebs or the exposed muscular layer of the worm after exfoliation of the tegument.