Abstract: This paper reports the observation on the ultrastructure of Schistosoma japonicum schistosomules with scanning and transmission electron microscopes. Schistosomules were transformed from cercaria by syringe meohanical method and by fresh serum incubation in vitro or skin penetration in vivo. The dynamic changes of schistosomules after being transformed for 3hrs and 12hrs were observed mainly in tegument and glands.1. Changes in tegument: The glycocalyx was reduced on the surface of the schistosomules that were transformed by mechanical method or skin penetration in 3hrs, and only its trace was seen on 12hrs worms. The glycocalyx was thin and discontinuous oh 12hrs serum schistosomules. The outer membrane of three kinds of 12hrs schistosomules changed into tri-, penta- or hepatalaminate structure. The inclusion bodies in tegument such as rod-shaped body, membranous vesicles and multilamellated body were present in 3hrs individuals and their number was larger in 12hrs worms. The anterior structure such as two crescents and sensory papillae were degenerated. The openings of acetabular glands were closed.2. Changes of glands: The head gland of Schistosoma japonicum schistosomules was unicellular, with a fundus possessing ducts filled with secretory granules. The secretory granules were nonmembranous but multilamellated in the ducts. Some 12hrs skin and artificial worms partly retained their secretory granules of head gland, especially those from mechanical method. The schistosomules of all three kinds did not exhaust their pre-or postacetabular glands completely in 12hrs.