A slaughtered 3 years old cow was diagnosed as bovine leukosis by postmortem inspection, agar gel immunodifusion (AGID) test, and polymerase chain reaction (PCR). It showed no special clinical signs except emaciation. Grossly, we observed enlargement of mediastinal and pelvic lymph nodes, and tubercle -like mass on pleura and lung surface, and masses on right atrium and ventricle.