Increased respiratory infection in Egyptian chicken flocks in the last few years with variable mortality, different clinical signs and increased economic losses urged us to study the viral causes of this problem. Examination of 100 chicken flocks suffered from respiratory signs, 485 live and freshly dead chickens (360 broilers, 114 layers and 11 breeder samples) were collected from 75 broiler, 23 layer and 2 breeder flocks at Sharkia governorate, Egypt. Out of the examined samples, 63% of suspected farms were positive for haemagglutination. Identification was by real time RT-PCR for selected 15 positive samples which suffered from high mortality and morbidity and/or drop egg production, the results revealed that 13 flocks were positive for AIV (7 flocks showed mixed infection with H5 and NDV and 6 flocks infected with H5 only) while one flock was positive for IBV. Partial gene sequencing was carried out for 5 positive samples 2 AIV (HA gene), 2 NDV (F gene) and 1 IBV (SP1 gene) to detect the genetic diversity. The phylogenetic analysis for 5 positive isolates revealed that H5N8 were related to Egyptian strains with nucleotide homology (96.5% - 99.3%), the identity percent was 91.8% to 98.2% compared with worldwide AIv-H5 isolates. The identity percent of NDV isolates 97.3% to 98.9% compared with Egyptian strains and 78.9% to 79.4% compared with vaccinal strains, while it was 82.1% to 97.6% compaired with worldwide strains. The IBV positive isolate was related to Egyptian strains with nucleotide homology 76.5% to 98.0% and it was 74.3% to 74.8% with vaccinal strains and was 71.6% to 97.3% compared with worldwide strains. The experimental infection with our isolate H5N8 (A/Chicken/Sharkia/MS001/2018) was carried out. Mortality percent and virus shedding were lower in vaccinated groups.