The nano-emulsion (NEs) is heterogeneous and self-emulsifying colloidal system dispersed in a liquid medium, the small size of the internal phase allows the system to overcome the problems related to the gravity force, that lead to avoiding creaming or sedimentation phenomena. Also, the low surface and interfacial tensions provide pest spreading and penetration of the active compounds thus may lead to increase the efficacy of the active ingredient compared to the micro-emulsion. Both the stored products insects, the rice weevil Sitophilus. Oryzae L. and the red flour beetle, Tribolium castaneum are very important as causing a lot of damage to many crops and other products. We aimed in this study to evaluate the toxicity of two nano-emulsions of Malathion against Sitophilus. Oryzae L. and Tribolium castaneum, which still used till now in Egypt for the control of stored products insects, these nano-emulsions are prepared under different conditions as subjected to different sonication power,50 and 75 KHz then named M50 and M75 respectively, M50 droplet size varied from 206.2 to 290 nm. While, M75 droplet size varied from 93.60 to 94.30 nm. There is no degradation on Malathion molecule was observed after either sonication powers 50 or 75 kHz as no observed changes in the retention time. Then examined against the both insect using film technique compared to commercial Malathion (EC57%). Our results indicated that M75 was more toxic than M50 and both were more toxic than the commercial Malathion. Potentiation factor of M50 and M75 were 2.11 and 3.75 fold against T. castaneum and 1.54 and 2.47 fold against S. Oryzae. And this may be results from the difference in particle size in the prepared nano-emulsions.