Abstract: In this study, arginine-glycine-aspartic acid(RGD) with tumor targeting was attached to the polyamidoamine dendrimers(PAMAM) with excellent biological properties as the nanocarrier labeled with radionuclide ¹³¹I. The pharmacodynamic properties of the labeled compounds in vivo and in vitro were evaluated, and the possibility of applying them to tumor-specific imaging and targeted therapy was discussed. The structure of the peptide Arg-Gly-Asp-Tyrosine-Cysteine(RGDyC) was determined by the chemical modification method, and then the double functional group(NHS-PEG-MAL, PEG) was introduced by the chemical method of click chemistry using “one pot two step” preparation. Nanocomposites were characterized by ¹H NMR and UV spectroscopy. And then particle size distribution and potential were detected. The morphology and size distribution were characterized by transmission electron microscopy(TEM). Chloramine T method was used to label ¹³¹I, and the labeling rate, marker stability and water partition coefficient were determined. The yield of RGDyC-PEG-PAMAM nanocomposite is 62.09%. The labeling rate of RGDyC-PEG-PAMAM is 94.68%-98.87%. The radiochemical purity of the marker in vitro is above 80%. Water partition coefficient, lg P(n-octanol/water) is -1.59±0.09. The designed RGDyC-PEG-PAMAM can successfully complete the ¹³¹I labeling with the chloramine T method. The preparation and labeling process is efficient and simple. The labeling product ¹³¹I-RGDyC-PEG-PAMAM has good stability, high hydrophilicity and good druggability. The results laid the foundation of pharmacodynamics study in vivo and in vitro, including further assess of the tumor cell uptake and growth inhibition in vitro, human tumor xenograft model therapy and tumor imaging. The results show that ¹³¹I-RGDyC-PEG-PAMAM can be used as a novel SPECT probe for tumor-specific imaging and targeted therapy.