In this observation, a case of perforated abomasal ulcer in a male, 27-day old, Swiss Brown calf is described with the clinical, macroscopical and microscopical findings. Clinical examination revealed dullness, anorexia, hypothermia, ruminal atony and tachycardia. At the necropsy, along with a small amount of abomasal content within the peritoneal cavity, perforated 2 out of 6 ulcers with sizes of 3-40 mm. at the pylorus were observed. Microscopic examination showed severe necrotic and acute inflammatory changes at the affected areas of pylorus and a diffuse fibrinous peritonitis.