A dead, female, 3 years old, squirrel monkey (Saimiri sciureus) was submitted and examined. Before death the monkey has showed lethargy, recumbency and inappetence since November 14, 2001 and died in November 17. Grossly much fibrin was deposited on the pleura of right lung, pericardium, and diaphragm(pleural part). And reddening of right lung was seen. Histopathologically lung showed severe fibrinous pleuritis, severe edema, thrombosis, and focal necrosis in parenchyma. Also much fibrin and mononuclear cells were deposited on the pericardium. In bacterial culture on the pleura and parenchyma of lung, and pericardium, B. bronchiseptica was isolated. Therefore we confirmed this case as the fatal case by B. bronchiseptica in squirrel monkey.