Dendrimers represent a unique class of nanostructures,playing important role in the field of nanobiotechnology1-4.Poly(amidoamine) (PAMAM) dendrimers were first to be synthesized and developed in Dow Laboratories between 1979 and 19855-6.Dendrimers are synthesized from branched monomer units in a step-wise manner,thus it is possible to precisely control their molecular properties,such as size,shape,dimension,density,polarity,flexibility,and solubility,by choosing different building/branching units and surface functional groups7.The large numbers of surface functional groups on dendrimers outer shell can be modified or conjugated with variety of interesting guest molecules8.Over the last several years,increasing interest has been attracted to the application of dendrimers as targeting carriers in cancer therapy and imaging9-11.Recent studies have demonstrated that the conjugation of special targeting moieties to dendrimers can lead to preferential distribution of the cargo in the targeted tumor-cells.The tumor-selective enhanced permeability and retention (EPR) effect of dendrimer made it an ideal targeting carriers in cancer therapy and MR image.In our lab 99mTc(CO)3 dendrimer PAMAM G5 - folic acid - 1B4M DTPA conjugate was synthesized with high yield (more than 95%),its excellent in vitro and in vivo stability provides great value for further bio-evaluation study.