Rabbits are highly susceptible to colibacillosis, and no treatment is able to control the disease effectively. Rabbits raised in a farm in Chonbuk province presenting persistent diarrhea and death were submitted for diagnosis. Ninety percent of the infected animals died; weanlings suffered the most mortality. Necropsies showed prominent hemorrhagic foci along the intestinal and cecal serosae. In histopathological examination, rod-shaped bacteria were observed in the necrotic areas of the tips of villi in the small intestine and neutrophils infiltration was found around the necrotic villous areas. The affected animals consistently yielded Escherichia coli isolates from the intestines. The isolated organism was atypically indole-negative and was nonserotypable using 62 known O group-typing sera. Further microbiological and epidemiological works to recognize and control colibacillosis infection in farmed rabbits in Korea is therefore critical.