Background/aims: Teleosts have blind tubes, so called pyloric cecum, connected with the anterior end of the small intestine. These pyloric ceca vary in number between１and more than 1000. However, the function of the pyloric ceca is not clear. Since they originate from that region of the intestine where bile and pancreatic juices are released, the ceca many form digestive compartments active in resorption of certain nutrients. We studied on the correlation between the histological components in pyloric ceca and their phylogeny by histological technique. Methods: Forty-six species teleosts that lived in fresh-water, brackish-water and sea, were collected from Shimane and Iriomote in Okinawa. Pyloric ceca were fixed with paraformaldehyde, and observed by light microscopy. Results: The pyloric ceca closely resembled the small intestine in structure, with a well-developed muscularis consisting mainly for circular muscle fibers. Mucus secreting goblet cells occurred among the epithelial cells. Conclusions: The present study indicates that the structures of pyloric ceca is concerned with phylogenetic classification. Our findings demonstrate that pyloric ceca may play a role in the duodenum.