Abstract: Plerocercoids of Spirometra mansoni were collected from muscles of the frogs. Specimens were treated following the routine procedure, embedded， sliced and stained. The ultrastructure of plerocercoid was observed with transmission electron microscopy. It was found that the wall of plerocercoid consisted of tegument and parenchyma. Thornshape microtriches distributed over the outer surface of the tegument. Matrix zone had a lot of granular discoidal bodies， vesicles， mitochondria and endoplasmic reticulum. Most of the mitochondria were near the basal membrane. Parenchyma zone consisted of muscular layer， tegument cells， parenchymal cells， excretory system, and so on. Many cytoplasmic pathways of tegumentary cells strech into muscular layer, suggesting that the tegument may be the absorptive site of nutrients.

Key words: Spirometra mansoni, Plerocercoid, Ultrastructure, Transmission electron microscopy