The entomopathogenic fungus, Beauveria spp. was isolated from house flies collected from different localities in various Egyptian Governorates. Flies were trapped from garbage piles, dairy and meat production processes on cattle farms and fowl farms. The study focused on Beauveria spp. as entomopathogens were widely used in recent decades as a biological control of the population of house flies, to avoid hazardous effects of insecticides on man animals, and natural eco-systems. Experimental laboratory trials were done using immersion of larvae on serial dilution of Beauveria spores reared different stages of the house flies. Infected larvae, pupae and adults were examined macroscopically for visible growth of fungi, before further studies using scanning electron microscope and histopathological methods, to investigate destructive impact of the fungus on the external and internal structures. The previous investigations revealed adhesion growth and propagation of the conidia on the cuticle of all stages, including compound eyes, setae of the legs, thorax, wings and abdomen of adults. Penetration and propagation of the conidia was evident in larval internal tissues causing lysis of fat cells, and of thoracic muscles of adults.