An organic compound labelled by using radioastatine was conjugated to a protein.211At reacts with the diazo-compound of para-aminobenzoic acid to yield para-astatobenzoic acid, which is separated by ether extraction and high performance liquid chromatography (HPLC) and then conjugated with IgG and bovine serum albumin (BSA) via an acylation reaction. The results of the animal experiments have shown that the211At-carbon bond is stable in vivo and the conjugate contains at least 40% of the initial activity of211At. Astatine-211 labelled proteins have also been prepared by direct oxidation with hydrogen peroxide or Chloramine-T. The separation of labelled proteins by Sephadex chromatography is very effective. The structure of proteins affects the labelling results and the yield of211At-BSA labelled by oxidation with hydrogen peroxide can be increased up to 96.4%.