TiO2 ultrafine particles are used as photo-catalysis. When ultrafine particles are exposed to hosts, they are invaded in alveolar, transferred to organs through blood vessels and may express biological effects. We administered TiO2 ultra-fine particles (5 nm, 100 nm) intratracheally to mice, and collected whole blood and removed organs (liver, lung, kidney, spleen and brain) after 1, 4 and 24 hours. The quantity of Ti in the blood and these organs was analyzed by PIXE (Particle Induced X-Ray Emission) or ICP/MS (Inductively Coupled Plasma-Mass Spectrometry). Compared to control mice, the quantity of Ti in the exposed mice was not different. Consequently, we observed the solution of dissolved TiO2 ultrafine particles by Scanning Electron Microscope, and observed the particles which aggregated. That diameter was about 1 microm. We concluded that the particles had aggregated before administration to mice, so they didn't invade the blood vessels or organs from the pulmonary alveolus in the lung.