Fourty fayoumi chicks (three days old) were inoculated with paeci lomyces species isolated from the lung of dead fayoumi chickens. The purpose was to study the pathogenicity and pathologic picture of this fungus in Fayoumi chickes. Focal granulomatus inflammation was observed in the serous membranes, Lung, liver and heart. gran ulomas in the liver, lung and heart were small in size and were frequently encapsulated. Paecilomyces species isolated from the lung of dead chickens were highly pathogenic for Fayoumi chicks causing deaths of 45% of it.