Two cases of cutaneous B cell lymphoma in Holstein cows aged 7 and 9 years are described. The animals, which were not infected with bovine leukemia virus, had neoplastic lesions not only in the skin but also in the abdominal cavity. The neoplastic cells were positive for surface CD79a and CD5 but not for terminal deoxynucleotidyl transferase (TdT), which is a marker for precursor T and B cells. The lymphomas, which were considered to be of mature B-1 B cell derivation, might be an adult counterpart of precursor B-1 B cell lymphoma in calves, because the calf lymphoma is similar to the current lymphomas in tissue distribution but expresses TdT as well as CD79a and CD5.