Ultrastructure of mature spermatozoon of Anisocoelium capitellatum is described with transmission electron microscopy. The description gave evidence of some characteristics of this digenean. The male gamete presents features allowing the distinction between A. capitellatum and other digenetic trematodes. It is characterized by original anterior and posterior extremities. The peripheral doublets appear prior to the central cores in the anterior extremity of axoneme. In the distal part of the spermatozoon, these ultrastructural features are also the first elements disappearing in the axoneme 1 and the last remaining in the axoneme 2. Another important peculiarity of the spermatozoon is the presence of three mitochondria.