Abstract: With the rapid development of molecular nuclear medicine, N-hydroxysuccinimidyl S-acetylmercap-toacetyltriglycline (NHS-MAG₃) as one effective bifunctional chelator has been used to radiolabel proteins, small peptides and DNA oligonucleotides with ⁹⁹Tc^m. The lable by the MAG₃-labeling method show high labeling efficiencies and high specific activities and hold desirable stability in vitro and in vivo. The binding of the lable with plasma protein is low. So many potentially useful radioparmaceuticals for diagnosis and therapy may be produced via the NHS-MAG₃ method.