Abstract: In July 2007, myeloblastosis and hemangioma cases associated with avian leukosis virus subgroup J (ALV-J) were first diagnosed in a layer chicken（150-day） flock in Shandong province. The main symptoms were characterized by runting-stunting and hemangioma. In the necropsy, almost all viscera tissues showed moderate to severe enlargement with diffuse gray-white nodules; Cutting open the hemangioma, blood effused and many myeloblasts were seen in blood smear. Histological examination indicated that the tumor cells proliferated in tissues mainly were myeloblasts with basophilia granules in cytoplasm; Intestinal gland epithelial cells and reticulocytes proliferated in lamina propria of alimentary tract; Hemangioma were typical sponge-like hemangioma. By immunohistochemistry (IHC) technique with ALV-J and REV monoclonal antibodies, the most intense staining of ALV-J antigen was found in the tumor tissues, liver, spleen, bone marrow, and proventriculus, while REV antigen was negative. The results indicated that myeloblastosis, hemangioma and other tissues tumors occurred in layer chickens were new dominance tumors induced by avian leukosis virus subgroup J (ALV-J).