Bacteriological examination of 320 dead and diseased bird revealed isolation of 180 isolates of P. multocida with an incidence of 56.25%. The morphological and biochemical characters of the isolated bacteria were determined by ordinary microscope and biochemical reactions. Five isolates of P.multocida were visualizated by electron microscope on the bases of difrrence  in mortality rate, symptoms and severity of the disease in normal infection, and the  capsular thickness of these isolates were determined. The capsule thickness of the examined isolates were 122 nm, 118 nm, 98 nm, 83nm, 81 nm, the virulence,resistance to serum complement and toxigenicity of these isolates were compared experamintaly in checkins.The laboratory examination of five isolates of P.multocida with different thickness revealed that there was a correlation between the capsule thickness and the pathogenecity and toxigenicity of the examined isolates.