As a molecular imaging is the most up-to-date technology in Nuclear Medicine, it has complicate ethical and regulatory problems. For animal experiment, we have to follow institutional animal care committee. For clinical experiment, we have to get approval of Institutional Review Board according to Helsinki declaration. In addition, approval from Korea Food and Drug Administration (KFDA) is essential for manufacturing and commercialization. However, too much regulation would suppress development of new technology, which would result in the loss of national competitive power. In addition, most new radioactive ligands for molecular imaging are administered to human at sub-pharmacological and sub-toxicological level. In conclusion, a balanced regulation is essential for the safety of clinical application and development of new technology. (Korean J Nucl Med 38(2):140-142, 2004)