Purpose: Ethylenediamine-tetramethylenephosphonic acid (EDTMP) has widely used chelator for the labeling of bone seeking radiopharmaceuticals complexed with radiometals. 153Sm can be produced by the HANARO reactor at the Korea Atomic Energy Research Institute, Taejon, Korea. 153Sm has favourable radiation characteristics T1/2=46.7 h, βmax=0.81 MeV (20%), 0.71 MeV (49%), 0.64 MeV (30%) and γ=103 keV (30%) emission which is suitable for imaging purposes during therapy. We investigated the labeling condition of 153Sm-EDTMP and imaging of 153Sm-EDTMP in normal rats. Materials and methods: EDTMP 20 mg was solved in 0.1 mL 2 M NaOH. 153SmCl3 was added to EDTMP solution and pH of the reaction mixtures was adjusted to 8 and 12, respectively. Radiochemical purity was determined with paper chromatography. After 30 min. reaction, reaction mixtures were neutralized to pH 7.4, and the stability was estimated upto 120 hrs. Imaging studies of each reaction were perfomed in normal rats (37 MBq/0.1 mL). Results: The labeling yield of 153Sm-EDTMP was 99%. The stability of pH 8 reaction at 60, 96 and 120 hr was 99%, 95%, 89% and that of pH 12 at 36, 60, 96 and 120 hr was 99%, 95%, 88%, 66%, respectively. The 153Sm-EDTMP showed constantly higher bone uptake from 2 to 48 hr after injection. Conclusion: 153Sm-EDTMP, labeled at pH 8 reaction condition, has been stably maintained. Image of 153Sm-EDTMP at 2, 24, 48 hr after injection, demonstrate that 153Sm-EDTMP is a good bone seeking radiopharmaceuticals.(Korean J Nucl Med 39(1):44-48, 2005)