Abstract: There were some chickens, collected from a layers farms of Qingdao in 2012, troubled with a disease which caused declining of weight and egg laying, and the clinic anatomise showed that the surfaces of viscus such as livers, lungs, kidneys and pancreases appeared many off-white tumor lesions. The pathological histology analysis result showed that these tumor lesions were of multifocal or multicentric, and the shape of these tumor cells were consistent. Identified pathological changes when infected Marek’s disease virus, the disease was identified to be the chicken lymphocytic leukemia, and some suggestions for the ways to prevent and control the disease were put forward.

Key words: chicken lymphocytic leukemia; visceral type of Marek’s disease; pathology; identification and diagnosis; prevention and control