Tc-99m-labeled antimony Sulfide nanocolloid was prepared by a new labeling method that involves room temperature reconstitution with (NaTcO4)-Tc-99m. Transmission electron microscope showed that the mean particle size was estimated to be mostly 7-15 rim. The labeling yield of Tc-99m-Sb2S3 was more than 99%. The stability of the labeled product was studied at room temperature and it was found to be excellent.