Avian Mannheimia hemolytica and Pasteurella multocida were investigated in different poultry farms at Beni-Suef governorate. Bacteriological examination of 160 samples which were taken from organs of freshly dead and diseased chickens revealed isolation of 50 (31.25%) isolates of Pasteurella.Spp., 16 (10%) isolates were Mannheimia hemolytica and 34(21.25%) isolates were Pasteurella multocida. Experimental infection was carried out on four weeks old Balady chickens which were inoculated with isolates of Mannheimia hemolytica and Pasteurella multocida separately, mortality rate in both reached to 80%. Samples were taken from dead chickens and examined bacteriolgically and histopathologicaly and Pasteurella. Spp. were reisolated from experimentally infected chickens. Antibiogram study with 10 types of chemotherapeutic agents revealed that both microorganisms were sensitive to ceftiofor, gentamycin and lincomycin + spectinomycin. The gross and microscopic pathologic lesions were variable in type and severity in field and experimentally infected cases. There was general hyperemia which most evident in veins of the abdominal viscera. Petecheal haemorrhages were frequently found and widely distributed. Livers of the most acutely affected birds were swollen and had multiple small focal areas of coagulative necrosis and heterophilic infiltration. Heterophilic infiltration also occurs in lungs and certain other parenchymotous organs.