Background The conventional pesticide formulations have many side effects on environmental. These effects were due to the huge quantity of pesticides used. Using of nanopesticide formulations can be reduced the quantity of pesticides used and subsequently decreased the cost of pest control and environment contamination. Results Indoxacarb and imidacloprid nanoparticles were developed. The size of nanoparticles ranged between 200 and 400 nm. The obtained results showed that the percentage of mortalities in second instar larvae of Egyptian cotton leafworm, Spodoptera littoralis were 95 and 75% in indoxacarb and imidacloprid nanoparticles, respectively. On the other hand, these percentages were 76.7 and 91.7%, respectively, with conventional formulations. In spite of one fifth of pesticide concentrations were used in nanoformulations, the LC50, s in nanoformulations were 2.9 and 15.9 ppm for indoxacarb and imidacloprid, respectively, compared to 34.3 and 66.5 in conventional formulation. The loading capacity in both indoxacarb nanoparticle and imidacloprid nanoparticle were 60.7 and 52.0%, respectively. Conclusion These results found that indoxacarb and imidacloprid nanoparticles were 12 and 4 times, respectively, more effective than indoxacarb and imidacloprid conventional formulations against the second instar larvae of S. littoralis. These results also showed that indoxacarb and imidacloprid nanoparticles can be used as effective formulations against the cotton leafworm larvae instead of the conventional formulation to reduce the environment contamination, control cost and pest population.