Many approaches for the application of nano-sized particles to the human body as nanotechnology have been recently developed. The size of nanoparticles is related to their useful character and also plays a key role in toxicity. Since this surface area can interact with biological components of cells, nanoparticles can be more reactive in than larger particles. In the present study, a fluorescence dye-labeled 50, 100 and 200 nm-sized silica particle suspension was intravenously injected into mice to identify the toxicity, tissue distribution and excretion of silica nanoparticles in vivo. Incidence and severity of inflammatory response was transiently increased with injection of 200 and 100 nm silica nanoparticles within 12h. But there was no significant response related to injection of 50 nm particles. The silica particles of 50, 100 and 200 nm were cleared via urine and bile. The 50 nm silica nanoparticles cleared to urine and bile than 100 nm and particles of 200 nm existed at lower concentration than other two smaller particles in urine and feces. Silica nanoparticles were trapped by macrophages in the spleen and liver and remained there until 4 weeks after the single injection.