The effect of neem, Azadirachta indica A. Juss, on ultrastructural alteration of larvae and puparia of the blow fly, Chrysomya megacephala (Fabricius) (Diptera: Calliphoridae) and house fly, Musca domestica (Linnaeus) (Diptera: Muscidae), was investigated in the laboratory by using neem extract containing 0.24% azadirachtin A. Larvae of both species exposed to single dipping with the neem product exhibited swelling of the integument in relation to the control as determined by scanning electron microscopy (SEM). Transmission electron microscopy (TEM) analysis revealed slight thickness of epicuticle, but intense thickness of procuticle. Multiple treatment of the larvae displayed noticeably swelling integument and bleb formation on the integument, indicating a dose-dependent relationshipPuparia of both fly species treated with neem product showed similar appearance under SEM and TEM analyses.