Patients with coronavirus disease 2019 (COVID-19) primarily develop respiratory symptoms, which sometimes can be serious. Respiratory failure is the most common cause of death from COVID-19. This disease also causes gastrointestinal (GI) symptoms. However, there are limited reports that severe GI disorders caused by COVID-19 can be fatal. Herein, we report three cases of fatal GI disorders caused by COVID-19. All patients developed severe pneumonia requiring mechanical ventilation and venovenous extracorporeal membrane oxygenation (V-V ECMO) support. The respiratory status improved, and the patients could be weaned off support. However, severe watery diarrhea (over a few liters per day) developed after the onset of respiratory failure. The CT, endoscopic, and pathological findings were similar to those observed in GI graft-versus-host disease (GI-GVHD). Despite various efforts, the GI disorders did not improve, and all patients died of multiple organ failures associated with sepsis due to intestinal mucosal disruption. COVID-19 can cause fatal GI disorders and may have similar characteristics to GI-GVHD. Further investigation will contribute to a comprehensive understanding of fatal GI disorders due to COVID-19.