The potential entry of nanomaterials into the water ecosystems increased following their increasing use. In addition to the direct effects of nanomaterials on aquatic organisms, they also affect the toxicity of other pollutants on aquatic organisms. This study assessed the presence of titanium dioxide nanoparticles (nTiO₂) in water on acute toxicity of silver nanoparticles (AgNPs) on zebra fish (Danio rerio). After preliminary tests, we simultaneously exposed the fish for 96 h to different concentrations of each of these nanoparticles so that, in each of the treatments, the concentrations of nTiO₂ were ten times the concentration of AgNPs. The results showed that the presence of nTiO₂ in water decreased the acute toxicity of AgNPs to more than three times in the zebra fish. The median lethal concentrations of AgNPs increased from 0.014 (in the absence of nTiO₂) to 0.044 (in the presence of nTiO₂). The reduction in toxicity of AgNps in the presence of TiO₂ nanoparticles in this study possibly happened due to decreased bioavailability of AgNPs by binding to the nTiO₂ and its deposition in water media.