Abstract.A 2-month-old male Holstein calf showed clinical signs of abdominal bloating, melena, and pain and was suspected of having a perforating abomasal ulcer. Necropsy revealed a large mass located preferentially around the abomasum and a large perforating abomasal ulcer on the pyloric antrum. Milky white masses of various sizes were also found in the abdominal cavity that consisted of agglutinated nodules ranging in size from a pinhead to a golf ball and were distributed on the surfaces of the liver, reticulum, omasum, abomasum, and diaphragm. Microscopic examination revealed that the masses were composed primarily of hyaline matrices, epithelioid tumor cells, and large atypical cells with hyaline droplets and/or vacuoles. Stromal hyaline matrices and hyaline droplets of the large tumor cells stained positive with periodic acid-Schiff stain. Tumor cells showed a positive reaction to anti-human alpha-fetoprotein, which is a marker of yolk sac tumors. These findings strongly suggested that the masses found in the abdominal cavity were yolk sac tumor, a rare germ cell tumor in cattle.