Titanium dioxide nanoparticles (TiNP) are widely used commercially and exist in a broad range of applications and consumer products such as exterior wall paints, antibacterial agents, white pigments, and sunscreens. We previously reported that the testis is a fragile organ against titanium toxicity as compared to the liver; TiNP has been shown to decrease both the sperm motility and the sperm numbers, that is, TiNP quantitatively and qualitatively change the sperm functions. There are, however, few reports regarding to the influence of TiNP on fertility ability. In this paper, we evaluated the influence of TiNP on fertilization rate using in vitro fertility (IVF) assay. Male C57BL/6J mice were administered orally with TiNPs (10 mg/kg or 100 mg/kg). Mice were sacrificed 24 hr after the administration. As a result, TiNP (10 mg/kg group) significantly decreased the fertilization rate. In the higher dose group (100 mg/kg), the degree was weaker than in the lower dose group. Our results indicate that TiNP reduces not only the sperm motility but also the fertility, and it will be useful information in considering the influence of TiNP on next generation.