Due to their wide range of uses in nanotechnology, nanomaterials are inevitably discharged into the environment in increasing concentrations. Titanium dioxide nanoparticles (TiO₂-NPs) and zinc oxide nanoparticles (ZnO-NPs) are believed to be inert and safe. Lepidopteran species are terrestrial insect in the environment and have been potential exposure of nanomaterial during life times. The reproductive toxicity of nanomaterials has been investigated mainly in mammals. To evaluate the effects of nanoparticles exposure on spermatogenesis, 5th instar larvae of sweet potato hornworm (Agrius convolvuli) were subcutaneously injected with each suspension of 10μl (100μg/ml) titanium dioxide nanoparticle (TiO₂-NPs) and zinc oxide nanoparticle (ZnO-NPs) or saline (control). Pupation and emergence were not affected by the injection. Each group of testes dissected at day-4 after pupation were examined by both optical and electron microscope. In the pupae on Day 4, the testes weight and the number of sperm bundles were significantly decreased in the ZnO-NPs group. TiO₂-NPs and ZnO-NPswere taken by phagocytosis of the cyst cell in pupal testes. In spermatogenesis advanced, various shaped and sized vacuoles were found in the nuclei of spermatogenic cysts, the nuclear chromatin of spermatids were uncondensed and some membranous structures were found in the nuclei of sperm bundles in the TiO₂-NPsand ZnO-NPs groups. Both TiO₂-NPs and ZnO-NPsgroups were shown the developmental deletion of spermatogenesis compared with the control group. A possible mechanism for this is that abnormal vacuoles disturbed the chromatin condensation, which resulted in the decrease of sperm bundles. These nanoparticles are known as inducers of intercellular ROS generation. The DNA damage may occur not only due to the direct interaction with DNA but also the indirect effects through ROS generation and the dissolved ions. The toxicity of manufacturedTiO₂-NPs and ZnO-NPs on insect spermatogenesis has never been demonstrated before this study.