Severe whipworm infestation, an exceedingly uncommon cause of gastrointestinal bleeding, has not been reported in Taiwan. The reported case concerns a 59-year-old female who had suffered from abdominal pain and passage of tarry stool for several days. Esophagogastroduodenoscopy was performed, and several roundworms were seen in the second portion of duodenum. After removal, the characteristic appearance of Trichuris trichiura was apparent. After exploratory laparotomy for intractable bloody stool, the result of operative findings and pathological reports also confirmed our diagnosis. This is a case presented of massive gastrointestinal bleeding in which the cause of bleeding was diagnosed before operation to be whipworm infestation by endoscopic examination. The clinical and pathologic characteristics of the trichuriasis are described, with a brief review and discussion.