Ultrastructure of mature spermatozoon of Purpura clavigera K?ster was observed by transmission electron microscopy. The mature spermatozoon contains two parts： head and tail. The head comprised an acrosome and a nucleus. The slim-cone shaped acrosome is about 2μm in length. The content in the acrosome is homogeneous and highly electron-densed. The morphology of subacrosomal space which is filled with highly electron-densed materials is similar to the shape of acrosome. The cylinder nucleus is about 16 μm in length. The content of the nucleus is highly densed. The nucleus is homogeneous. The endonuclear channel extends to the front part of nucleus from caudal nucleus. The inner diameter of the endonuclear channel is about 0.2 μm. The basal body is formed by a single centriole which is located at the apex of endonuclear channel. The “9 ＋ 2” arrangement of axoneme emitting from basal body run through the whole sperm. The tail is composed of mid-piece, principal piece and end piece. The chondriosomal mantle which is formed by filar mitochondria enwraps the “9＋2” arrangement in the middle piece. The thickness of every mitochondrial gyration is about 0.1μm . The distance between gyration is equidistant. No chondriosomal mantle exists in the principal piece, only glycogen particle mantle surrounds axoneme. In the end piece, only plasma membrane surrounds the axoneme. The similarities and differences of the sperm ultruastructure between Purpura clavigera K?ster and other Prosobranchia including Archaeogastropoda, Mesogastropoda and Neogastropoda are discussed. The evolving trend of Prosobranchia sperm can be seen obviously by comparing the structure. The sperm structure of Prosobranchia changes from “primitive type” which was found in Archaeogastropoda to “modified type”, the latter were found in Mesogastropoda and Neogastropoda. The head of Archaeogastropoda sperm that undergoes external fertilization tapers. The rear part of the nucleus has a posterior nuclear pocket. The proximal and distal centrioles are located in posterior nuclear pocket. The distal contrioles emits axoneme and finally forms the tail. The simple tail contains a short mid-piece and a slim end piece. Several mitochondria enwrap centriole in middle piece. In the end piece, only plasma membrane surrounds the axoneme. The head of sperm in Mesogastropoda and Neogastropoda animals which undergoes intemal fertilization is slim. The tail is composed of middle piece, principal piece and end piece. The chondriosomal mantle which is prolonged and originated from mitochondriasurrounds the axoneme. In the principal piece, the “9＋2” axoneme was surrounded by glycogen particles. The ultrastructure of the end piece is the same as Archaeogastropoda animals. Chondriosomal mantle is formed to cumulate more energy and the glycogen particle mantle can supply more energy. The formation of chondriosomal mantle and glycogen particle mantle in the sperm tail meets the energy requirement for the intemal fertilization, and it also shows us an important morphological feature during the sperm evolution. Purpura clavigera sperm ranks higher evolutionary status in Prosobranchia than other species. The following aspects should be considered when we pursue Prosobranchia species evolution： The existence or not of acrosome, the fine feature of acrosome, the shape and the length of nucleus, the number, morphology and the arrangement of mitochondria in the mid-piece, and the existence or not of glycogen particle mantle. The comparative study on representative species sperm structure in different order, family, genus of Prosobranchia can help us in revealing the evolutionary trend of Prosobranchia, and also in analysing the evolutionary relationship of different order, family, genus and species.