Abstract: Objective To investigate the application of 153Sm labeled cytosine in tumor metabolic imaging. Methods The cytosine was labeled with 153Sm by DTPA coupled method, the final product was C-DTPA-153Sm. The labeled product was then purified. The determination of acute toxicity, in vitro stability, plasma pharmacokinetics in rabbits and imaging of cell and in tumor-bearing mice of radiolabeled cytosine were carried out. Results The results of examinations and animal experiments showed that the C-DTPA-153Sm was free of bacteria, pyrogen and toxic agents, and it could be concentrated at the tumor site in tumor-bearing mice. Conclusion C-DTPA-153Sm metabolic imaging might be used to evaluate the tumor growing status and may have important clinical value.