Abstract: A method for labelling G-immunoglobulin and monoclonal antibody with rare earth radionuclides is reported. In this labelling process cycloanhydride of TTHA is employed as a bifunctional chelating conjugate to make prior linkage of TTHA to globulin, then followed by the metal chelation.The influencing parameters of labelling globulin with rare earth, such as metal to TTHA ratio, pH value and labelling time are investigated in detail. Through the whole labelling process the immunoreactivity of the labelled compound is well preserved.