Abstract: The aim of this study is to evaluate the potential applicability of radioiodine-labeled human recombinant 36 kDa protein Annexin Ⅴ prepared in domestic conditions as an imaging agent for diagnosis of apoptosis. Experimental conditions for labeling of Annexin Ⅴ with~(125)I or~(131)I by Iodo-Gen method are optimized with respect to the concentrations of Iodo-Gen and the protein, reaction time, temperature, and pH value. Under the recommended conditions a labeling yield of higher than 80% may be achieved. The radiochemical purity of the labeled protein is increased to 95% or higher after purification with gel chromatography. The labeled compound~(125,131)I-Annexin Ⅴ prepared in this way is proved to be stable within 40 h at room temperature. The animal experiment with normal mice shows that~(125,131)I-Annexin Ⅴ is quickly distributed in whole body after injection and mainly accumulated in liver, kindneys and spleen. The clearance from blood is very fast. In vivo deiodination is also observed. Our in vitro experiments with Balb/C mouse thymus cells indicate that~(125,131)I-Annexin Ⅴ maintains high affinity to dexamethasone-induced apoptotic cells, K is 8.53 nmol/L, RT is 1.23×10~6 binding point/cell.