The three dimansional (3D) nanostructure of particulate in rubber (NR) were observed for the first time by use of 3D transmission electron tomography. The method enabled us to visualize and evaluate structural charachteristics in 3D space, such as the size and the volume of in situ silica generated in the NR matrix by the sol-gel reaction of tetraethoxysilane, at nanometer scale resolution.