Pathogenicity of eighteen local viral isolates of hydropericardium hepatitis syndrome (HHS) in broiler were studied in 1 & 21 days old age chickens using intraperitoneum injection and oral administration .According to macroscopic and histopathological changes , four isolates were found to be highly pathogenic in inducing pathognomic lesions of HHS than others which were characterized as moderate pathogenic isolates . The results showed that I/P injection of 21days old chicken lead to histopathological changes in affected organs clearear than other routes of inoculations.