To evaluate the acute lung toxicity of intratracheally instilled nano-titanium dioxide (TiO2) in Kunming mice, healthy adult Kunming mice were randomly grouped by their body weights (5 mice in each group). The lungs of mice were intratracheally instilled with 1 mg/kg•bw or 10 mg/kg•bw of nm-TiO2. The control group was intratracheally instilled the same volume physiological brine. After exposure of 1, 7, 14 and 28 days, the bronchoalveolar lavage (BAL) fluid and lung tissue were collected. The indexes in BAL fluid were examined. Lung tissues were assessed by histopathology. The results showed that all indexes of 10mg/kg•bw groups were obviously higher than those of the control group and the group of nano-1mg/kg•bw. Activities of LDH on the 1st, 7th, 14th and 28th day post-exposure (pe), contents of MDA on the 1st, 7th and, 14th day pe and TP on the 1st and 7th day pe as well as the amount of leukocyte on the 1st and 7th day pe of 10mg/kg•bw groups were significantly different compared with control groups (P<0.05).There were no obvious changes observed in the activity of ATP within groups (P>0.05). Histopathology found that lungs of 10mg/kg•bw groups presented great increase in pulmonary inflammation. Many TiO2 particles were still clearly found in the interstitium at 28 days pe. In contrast, low-dose instillation had a low risk potential for producing adverse pulmonary health effects. We conclude that the inflammatory reaction gradually eased after 28 days pe. Under the same experimental condition, the effect of lung injury was severer in high-dose nano-TiO2 than low-dose nano-TiO2.