Abstract: A viral strain, designated as FJ1674, was isolated from dead chickens that showed hydropericardium syndrome. The gene fragment of the strain, which lacked the hemagglutination activity, could be amplified by the specific primers of avian adenovirus serotype 4 against those of the viruses of avian influenza, newcastle disease, avian infectious bronchitis, avian encephalomyelitis, avian leukemia, infectious bursa, avian metapneumo, and inclusion body hepatitis. Thus, FJ1674 was believed to belong to avian adenovirus serotype 4.The sequencing analysis revealed its high homology (99.4%-100%) between FJ1674 and its counterpart in GenBank. The phylogenetic analysis also showed that FJ1674 was close to viruses of the same serotype, and could be subdivided into the same isolate cluster.