A 49 year-old man drank paraquat 7-8 fold of human fatal dose, and died of severe respiratory failure in 24 days in spite of intensive therapy. The autopsy revealed diffuse pulmonary fibrosis caused by prolonged intoxication of paraquat. An interesting finding was many raised plaques from 1 mm to 10 mm in diameter, observed in whole colon. Histologically, these plaques were composed of necrotic mucosa ("pseudomembrane"), disrupted crypts and edematous submucosa with fibrin education, intervening in normal colon tissue with sharp margins, and diagnosed as non-antibiotic-induced pseudomembranous colitis. Since the edematous submucosa of the raised plaque had a stratified fibrin education around a dilated capillary, it was speculated that the vessel injury by paraquat might play a role in the pathogenesis of pseudomembranous colitis.