Abstract: Several representative bifunctional chelating agents (BFCA) molecules which can coordinate with Re(CO)3(H2O)3+ were synthesized. On the NCA level, the ligands allow labelling yields >95% with 188Re(CO)3(H2O)3+ under mild reaction conditions. Incubation of the corresponding 188Re complexes in PBS buffer and human serum at 37 ℃ reveals good stabilities. Decomposition product is main 188ReO-4. The routine kit-preparation of the precursor 188Re(CO)3(H2O)3+ in combination with tailor-made ligand systems enables the organometallic labelling of biomolecules with unprecedented high specific activities.