A specimen kit having a tiny chamber is disclosed for a specimen preparation for TEM. The space height of the chamber is far smaller than dimensions of blood cells and therefore is adapted to sort nanoparticles from the blood cells. The specimen prepared under this invention is suitable for TEM observation over a true distribution status of nanoparticles in blood. The extremely tiny space height in Z direction eliminates the possibility of aggregation of the nanoparticles and/or agglomeration in Z direction during drying; therefore, a specimen prepared under this invention is suitable for TEM observation over the dispersion and/or agglomeration of nanoparticles in a blood.