Gymnophalloides seoi, a new intestinal trematode of humans transmitted by oysters on a southwestern island of Korea, drew medical attentions because of its possible relationship with evoking pancreatitis or other pancreatic diseases. We experienced two interesting cases of G. seoi infection who were accompanied with diabetes mellitus. In routine stool examination, eggs of a gymnophallid were detected from two patients, and after treatment with praziquantel and purgation, 772 and 10 adult flukes were recovered respectively. They were identified as G. seoi. The first patient was a 62-year old man who lived in Mokpo, nearby the known endemic area, and the second patient, a 54-year old woman who lived in Inchon. They used to eat raw oysters. It should be ruled out that G. seoi infection has some relationship with pancreatic diseases.