¹College of Animal Science, Yangtze University, No. 88 Jingmi Rd., Jingzhou 434025, Hubei, P. R. CHINA DOI : 10.9775/kvfd.2017.19079 Avian leukosis virus subgroup J (ALV-J) infection can cause tumors and immunosuppression, which has made huge financial loss in the poultry industry. More and more new pathogenic avian leukosis virus, which were recombined from exogenous avian leukosis virus and endogenous retrovirus viruses were isolated from China and other regions in the world. To uncover the characteristic of the potential recombinant elements, we analyzed the genomes of avian endogenous retrovirus ev/J in ten chicken breeds in China. Six of the ten chicken breeds contained two sizes of ev/J (3.8 kb and 2.2 kb) and the other only contained 3.8 kb ev/J. The ten 3.8 kb ev/J were much closer to type I, II and III ev/J prototypes, while the six 2.2 kb ev/J were close to type IV ev/J prototype in the phylogenetic trees. Moreover, three novel deletion fragments were identified in the sixteen ev/J in chicken flocks in China, which made most of the ev/J (10/16) significantly different from the four ev/J prototypes. The emergence of these novel deletions resulted in the diversity of ev/J in chicken breeds in China, which may become the source of further recombination of avian leukosis viruses (ALVs), especially the exogenous ALV subgroup J. Keywords : Avian endogenous retrovirus, ev/J, Avian leukosis viruses, Genome, Chicken breeds