Abstract: The cyclic RGD dimer was modified with 2 PEG₄ between RGD motifs in the RGD dimer, as well as with 1 PEG₄ between the RGD dimer and chelator HYNIC. The in vitro and in vivo characteristics of ⁹⁹Tc^m labeled different RGD dimer were evaluated, including IC₅₀, lg P, pharmacokinetics and biodistribution. It is demonstrated that introducing of 2 PEG₄ between RGD motifs significantly enhances the binding affinity of RGD dimer and integrin α_vβ₃; the introducing of PEG₄ improves the hydrophilicity of ⁹⁹Tc^m-labeled RGD dimmer. ⁹⁹Tc^m-HYNIC-2PEG₄-RGD dimer possess better properties, with the value of further development for integrin α_vβ₃ positive tumors imaging.