Abstract:Avian leucosis virus (ALV) is one of the most variable viruses， and has many subgroups. Its subgroup J (ALV-J) is much more transmissible and pathogenic than all other subgroups. It was demonstrated ALV-J has a great multiplicity of its quasispecies even in the same stock or in the same isolates of a same strain. During the first decade since its first isolation in 1988， it mainly infected white broiler chickens causing myeloid leukemia. But in the recent decade， it gradually spreads into layers， Chinese “yellow” chickens and local indigenous breeds， and caused tumors in various tissues with different types of cells. Apparently， it was closely related to the genetic evolutions of ALV-J. In this review， gp85 sequences of 147 ALV-J strains isolated from different types of chicken farms in China and other countries during the last 25 years were collected and summarized for analysis and comparison of homology relationships and their evolution under different selective pressures. LTR (long terminal repeat) fragments were also analyzed and compared for some strains. The information would be helpful to better predict further evolution trends of ALV-J and make more effective measures for control and prevention of ALV infection in chickens.