In this study one hundred Awassi sheep were examined clinically and bacteriologically for isolation and identification of the bacterial agents of otitis externa in sheep. The main clinical signs appeared included weakness, pale mucus membrane, auricular discharge, cough, anorexia, emaciation, and nasal discharge. Results revealed isolation of bacteria from (45%) examined swabs. The most being from right ear. Younger animals were more frequently infected than older animals. Pseudomonas aeruginosa, Staphylococcus aureus, Mannheimia haemolytica, Staph. epidermidis, Pasteurella multocida, Streptococcus spp., Acintobacter spp., Escherichia coli and Klebsiella pneumonia were isolated. The results revealed that the most bacterial isolates were resistance to the bactericidal effect of the normal serum included Streptococcus pneumonia, Staphylococcus aureus, Mannheimia haemolytica. While the most bacterial isolates were produced hydroxymate siderophore included Staphylococcus aureus, Mannheimia haemolytica, Streptococcus pneumonia. The obtained results indicated to the importance of determination of serum resistance as a bacterial virulence factor in otitis externa in sheep.