Avian adenoviruses can be subdivided into three groups: group I, group II and group III. Group I inclides the conventional group I adenoviruses, or fowl adenovirus (FAV-1-12) isolates from chickens, turkeys, geese, and other avian species, which share a common group antigen. The role of group I avian adenoviruses as pathogens is not well defined. They appear to have a role as a secondary pathogens in association with other diseases. It has been found that birds were reinfected with the same strain after 8 wk, eliciting a secondary response of both neutralizing and precipitating antibodies; virus excretion also occurred despite humoral antibody. So, if the virus can be constructed into a vector to express foreign protein, it would induce strong immunity against the foreign protein in chickens for long time. There were some preliminary research results on FAV vector in foreign countries, while there was few research progress in our country,.At present, there were more research progress on recombinant human adenovirus vector. Early region 1, 3 and 4 (E1,E3,E4) are the common targets for insertions of foreign genes in mammalian Adv-based vectors. Since it is not clear in location of El, E3 and E4 regions in FAVs genome, alternative strategies had to be explored for construction of FAV-based vectors. Here, we demonstrated the isolation and identification of a strain of fowl adenovirus group I virus (FAVI-JS) from clinical healthy chickens, the selection of non-essential region of FAVI-JS, the replicability and pathogenicity of recombinant FAVI-JS expressing the enhanced green fluorescenceprotein (rFAVI-eGFP) in chickens, we then inserted fusion protein of Newcastle disease virus (NDV) into the the system of recombinant fowl adenovirus to confirm whether the system have the capability to express foreign protein.1 Identification of an isolate of fowl adenovirus group 1 virusAn isolate of fowl adenovirus group I virus (FAVI-JS) from clinical healthy chickens was isolated and identified by virus morphology, cytopathogenic effect (CPE) and sequence analysis. The virus particles showed non-enveloped, about 70~80nm in diameter. It could't agglutinate red blood cells (RBC) of chicken, duck or goose, but could agglutinate rat cells. The virus caused CPE in chicken embryonic kidney (CEK) cells. L, R, ITR fragment of the viral genome were emplified by PCR. The sequences of these three fragments were analyzed and compared with the relevant parts of CELO virus, FAV-1, FAV-A and FAV-8 obtained from GenBank. The results showed that the three fragments of these viruses shared more than 96 percent nucleotide sequence homology to FAVI. The phylogenetic tree inferred from ITR sequences, which was important in genetic to adenovirus, showed that FAVI-JS and fowl adenovirus group I viruses converged into a lineage, especially closed to serotype 1 virus. The virus from group III shared the other lineage. From these results, we can confirmed that FAVI-JS is a member of group I fowl adenovirus.2 Identification of Non-essential Region for Fowl Adenovirus Replication of JS StrainThe non-essential region of a strain of fowl adenovirus group I virus isolated (FAVI-JS) from chicken was identified. The left terminal (L fragment) and right terminal (R fragment and ITR fragment) of virus genome were amplified by PCR respectively. PCR products were cloned into pGEM-T easy vector. L fragment, ITR and R fragment were then cloned into pHC cosmid to construct pHC-FAVI-R-ITR-L. The enhanced green fluorescence protein (eGFP) coding sequence was cloned between R fragment and ITR fragment to construct transfer vector pFAVI-eGFP. Then the pFAVI-eGFP was transfected CEK infected with wt-FAVI-JS. The recombinant FAVI (rFAVI-eGFP) was recovered by homologous recombination in CEK between wt-FAVI-JS genome and pFAVI-eGFP DNA. rFAVI-eGFP was purified by serial dilution of the supernatant of transfected cells. These results showed that the region between r fragment and ITR fragment was dispensable for virus replication in vitro.rFAVI-eGFP could ag