Abstract: Objective To determine the short-term and long-term distribution of nano-Fe₃O₄ and nano-TiO₂ in mice.Methods Nano-Fe₃O₄ and nano-TiO₂ were injected into abdominal cavity of the mice and their contents in the tissues were detected by AAS and ICP-OES,respectively.Meanwhile,histopathological evaluation was carried out.Results Nano-Fe₃O₄ was distributed in heart,spleen,liver,lung,kidney,brain in turn within 24 hours after the injection.After repeated injection for 10 days,the accumulation of iron in the organs studied was slight compared with single-dose injection,indicating that iron was eliminated fast at the exposure of 100mg/kg.Nano-TiO₂ was also well tolerated at the concentration of 300mg/kg with little accumulation mainly in spleen and liver.No Fe or Ti-positive pigment was observed in macrophages of the heart,spleen,liver,lung,kidney,brain,and spermary.Conclusion The results of the study demonstrats that the potenitial hazard of nano-Fe₃O₄ and nano-TiO₂ is low in mice.