Abstract: Objective 　To investigate the biological activity of tumor vascular targeting agent s (RGD10 、F56 and K237) labelled with 131 I and their specific localization in tumor. Methods 　Tumor vascular targeting agents were labelled with Iodogen method and subsequently separated with Sep-Pak C18 column. Then, their immunoreactive fraction and affinity constancc were determined after HUVECs trials. Their specific localization in nude mice bearing human A549 lung adenocarcinoma were observed and compared by eZscope. Results 　The immunoreactive fraction of 13 131 I-RGD10 、131 I-F56 and 131 I-K237 was 42. 7 %、55. 1 % and 44. 5 %, respectively. Their affinity constant with HUVEC was 9. 41 ×107L/ mol 、3. 87 ×107L/ mol and 5. 98 ×107 L/ mol, respectively.131 I2 RGD10 located in tumor more densely than 131 I-F56 and 131 I-K237 af ter they were injected into the tail vein of nude mice. Conclusion 131 I-RGD10 may be a targeting agent in radionuclide imaging of tumor early diagnosis.