Abstract: This article presents an indirect method of labelling proteins. an organic compound is labelled by radionuclide and then the compound is conjugated to a protein. The α- particle emmiting nuclide ~(211)At was reacted with diazo-compound of para-aminobenzoic acid to obtain para-astato-benzoic acid. The labelled compound was separated by ether extraction and reversedphase high performance liquid chromatography, and then was conjugated with IgG or bovine serum albuminr(BSA) by an activating reaction of carboxy. Sephadex G-75 column was used to separate the labelled protein from reactive products and the labelling yield was determined by the relative method comparing radioactive counts. The conjugate contained at least 40％ of the initial activity of ~(211)At. The results of the animal experiments showed that the conjugate was stable in vivo. The retention of ~(211)At in blood of mice was much greater in the ~(211) At-IgG treated mice than in the Na~(211)At treated mice, implying that the bond between the IgG and astatine was stable in vivo.