The blowfly, Chrysomya megacephala (Fabricius), and housefly, Musca domestica Linnaeus, are ubiquitous insects that have the potential to spread a variety of pathogens to humans and livestock. Pest management techniques for populations of these flies are needed. Currently, bioinsecticides, particularly those derived from plant origin, have been increasingly evaluated in controlling populations of medically important insects. In this study, an attempt was made to evaluate the efficacy and biological activity of a commercially available neem extract, containing 0.24% azadirachtin A, against C. megacephala and M. domesitca. Laboratory bioassays were performed using the feeding method of mixing neem solutions with fresh beef, once or multiple times, as food for rearing third instar. The laboratory tests showed that neem products significantly reduced larval and pupal survival, adult emergence, pupal weight, adult wing length, and fecundity on the subsequent generation, in a dose-dependent manner in both species. Efficacy was observed in the first generation and could extend to the second generation. Despite these reductions, reduction in total adult longevity was not evident for larvae fed once on neem solutions with fresh beef, and slightly earlier (approximately 1 week) mortality was observed in both species when they were fed as larvae on multiple doses. Adverse effects of this neem-based product toward M. domestica were slightly greater than those in C. megacephala. These data reinforced the efficacy of neem extract in reduced adult emergence and anti-fecundity in the subsequent generation. However, neem extract induced only low to moderate larval and pupal mortalities.