Objective To study acute toxicity of nanometer titanium dioxide to the liver and kidney of mice. Methods 20 KM mice (22-26 g) were randomly divided into two groups, the control group and the experimental group, TiO2 (20-30 nm) suspension (single dose of 5 g/kg body weight) was given to mice by a single oral gavage, the mice in the control group were given the physiologicalsaline. 14 days after the treatment, the mice were sacrificed and the serum were collected to evaluate the levels of ALT(alanine amino transferase), AST(aspartate aminotransferase), ALP(alkaline phosphatase), UA(uric acid), Cr(creatinine),BUN(blood urea nitrogen), CK(creatine kinase), LDH(lactate-dehydrogenase), ?-HBDH(alpha-hydroxybutyrate dehydrogenase), TBIL(total bilirubin levels). The tissues of the liver and kidney were excised and were embedded in paraffin blocks, hematoxylin-eosin (HE) staining for further histopathological diagnosis. Results The serum ALT, ALT/AST, BUN, LDH and ?-HBDH of the TiO2 group were statistically higher than those in the control group (P