Tee present study was carried out on 10 parent chickens flocks collected from different provinces. The examined cases were classified into 47 commercial layers and 198 broiler parents to study the gross and microscopical lesions of different tumors induced by avian leukosis subgroup-) (ALV-J) in broiler breeders and layers flocks. , Serological tests were conducted on 245 serum samples to detect the antibodies of ALV-J. Polymerase chain reaction PCR was carried out on tis- ‘we samples to confirm the presence of DNA of ALV subgroup J. Myeloid leukosis was recorded in four broiler flocks induced by the novel subgroup-J of ALV. Pathological findings of infected parent chickens flocks revealed multiple neoplastic nodules in different organs including liver, kidney, gonads, intestine, skeletal muscle and bone. Histologically, the main constituent of tumor lesions was mature and immature myelocytes. Nephroblastoma was considered as the first recorded cases in Egyptian broiler parent flocks affected with ALV subgroup J. The results of this work concluded that the histopathological examination plays a crucial and decisive role in diagnosing different types of neoplasm caused by avian leukosis virus subgroup-J. The application of PCR test verified the presence of DNA of ALV-J that induced the tumors of myeloid leukosis.