The Ultrastructural effects of chlorpyrifos and phenthoate on midgut of third larval instar of Chrysomya albiceps was illustrated with the aid of transmission electron microscope. It was clear that chlorpyrifos considered to be most potent than phenthoate. The number of pupae and emerged adults were reduced after treatments with all concentrations of the two insecticides. There was a predominance of males over female (ratio, 4.5:1), respectively after treatment with 15 ppm chlorpyrifos. Based on ultrastructural changes, after treatment with phenthoate, densely compressed cells with irregular shrank nucleus that has fragmented nucleoli and lacked condensed chromatin were observed in the midgut cells. The rough endoplasmic reticulum becomes swallowed. The microvilli clumped and shrunk. After treatment with chlorpyrifos, Numerous number of large vacuoles observed at the periphery of the midgut cells. The mitochondria show different degrees of deformation from clumping of cristae to rupture of mitochondrial membrane.  The cells of midgut possessing short, shrunk or atrophied microvilli. Lysis of most cellular organelles is the most characteristic features after chlorpyrifos treatments.