Abstract: Objective To evaluate the toxicity of nano-titanium dioxide(TiO₂)with the model organism of Caenorhabditis elegans(C.elegans).Methods C.elegans were exposed to 0.1,1.0 or 10 μg/L of 5nm,35nm,and 300nm TiO₂ primary particles,respectively.The toxic effects were determined with endpoints of development,reproduction,and locomotion behavior.Results The exposure of 5nm TiO₂ primary particles lengthened the generation times,decreased the brood sizes and suppressed the locomotion behaviors at the exposure dose above 1.0 μg/L(P<0.05).The generation times were significantly lengthened when C.elegans were exposed to 0.1g/L of 5nm TiO₂ .C.elegans showed the decreased brood sizes and swings when exposed to 35 nm TiO₂ primary particles of 1.0 μg/L and 10g/L(P<0.05).There was a significant difference in body bends between the high-dose group and the low or moderate dose groups with the exposure of 300nm TiO₂ (P<0.05).Conclusion The development,reproduction,and locomotion behavior of C.elegans are affected by TiO₂ nanoparticles exposure and the effect correlates with the size and concentration of TiO₂ nanoparticles.