Abstract: Diethylenetriaminepentaacetic acid (DTPA) used as a bifunctional chelator coupling with human serum albumin (HSA) to improve the in vivo stability of radionuclides labeled HSA has been studied. The DTPA anhydride is synthesized and added to aqueous HSA as solid. The optimum condition of DPTA coupling with HSA and the labeling of 99Tcm with DTPA coupled HSA have been investigated. Potassium biphthalate (pH 5) is the best buffer among Hepes,phosphate and citrate buffer. nDTPA/nHSA more than 3 and nsn2+/nDTPA less than 0. 5 are the suitable labeling conditions (when HSA concentration is 15 mg/ml). Biodistribu-tion studied in mice shows that 99Tcm labeled DTPA-HSA is stable in blood. The DTPA/HSA coupling efficiency is detected by the labeling of 114Inm, which is produced by 113 In neutron irradiation.