This study aimed to evaluate the acute toxicity of intravenously administrated amorphous silica nanoparticles (SNPs) in mice. The lethal dose, 50 (LD50), of intravenously administrated SNPs was calculated in mice using Dixon's up-and-down method (262.45±33.78 mg/kg). The acute toxicity was evaluated at 14 d after intravenous injection of SNPs at 29.5, 103.5 and 177.5 mg/kg in mice. A silicon content analysis using ICP-OES found that SNPs mainly distributed in the resident macrophages of the liver (10.24%ID/g), spleen (34.78%ID/g) and lung (1.96%ID/g). TEM imaging showed only a small amount in the hepatocytes of the liver and in the capillary endothelial cells of the lung and kidney. The levels of serum LDH, AST and ALT were all elevated in the SNP treated groups. A histological examination showed lymphocytic infiltration, granuloma formation, and hydropic degeneration in liver hepatocytes; megakaryocyte hyperplasia in the spleen; and pneumonemia and pulmonary interstitial thickening in the lung of the SNP treated groups. A CD68 immunohistochemistry stain indicated SNPs induced macrophage proliferation in the liver and spleen. The results suggest injuries induced by the SNPs in the liver, spleen and lungs. Mononuclear phagocytic cells played an important role in the injury process.