As an emerging model for toxicological studies, zebrafish has been explored for nanotoxicity assessment. In addition to endpoint examination of embryo/fish mortality and/or developmental disorders, molecular analyses of differential gene expression have also been employed to evaluate toxic effects associated with the exposure to nanomaterials. Here, we describe zebrafish-based assays, including both embryo and adult, for evaluation of nanotoxicity caused by metal oxide nanoparticles (NPs), in particular, zinc oxide (ZnO) and titanium oxide (TiO(2)) nanoparticles.