The present study was conducted to investigate bacterial diseases causing mortality in the first week of broiler's chick life on broiler poultry farms in Dakahlia Governorate. A total of 240 samples (105moribund chicks and 135 dead chicks) resembles different breeds (Avian,Cobb, Hubbard, Baladi and Saso) , different ages(1-7d.), different housing capacity (5.000:20.000) as well as different farm districts in Dakahlia Governorate were collected during the experiment period (2012-2015). The isolated bacteria from these samples were identified by culture CHARacter , biochemical tests and serological identification. The predominant isolated bacteria were Salmonella (75%) identified as 3 isolates of Salmonella Enteritidis one isolate of Salmonella Typhimurium , one isolate of Salmonella Kentucky one isolate of Salmonella Tamale and E. coli isolates (25%) identified as two isolate of E. coli (O)serogrroup. The isolated strains of Salmonella and E. coli were inoculated into susceptible one day old chicks by two routes (oral and I/p) route. The clinical signs, PM lesions, histopathological lesions and performance profile of each subgroup revealed that chick mortality were recorded with clinical signs and septicemic pictures of most inoculated groups except control group. Mortality rate was higher in (I/p) inoculation than (oral) inoculation . Histopathological lesions proved signs of severe congestion in liver, lung, and other tissue samples. Growth performance parameters proved that there were significantly lower feed intakes, mean body weight gain all over the experimentation period (four weeks) in all groups in comparison with control group.