Integrin α3β1 has been shown to be a novel candidate target for the imaging and specific therapy of non-small-cell lung cancer. We have previously reported on a peptide containing a novel motif of NGXG that specifically binds to the integrin α3 receptor on lung cancer cells using a one-bead one-peptide combinatorial library. In this study, we developed the peptide cNGEGQQc-based therapeutic agent labeling with radionuclide iodine-131 (131I) and evaluated its characteristics including stability, biodistribution, antitumor activity, and safety. The results showed that 131I-cNGEGQQc was stable in serum. Furthermore, the biodistribution of 131I-cNGEGQQc was determined in normal mice and rabbits. In-vivo biodistribution studies showed that radiolabeled peptide in the kidney was significantly higher than that in other organs. Nude mice bearing lung cancer cell xenografts (H1975 and L78) were used as an in-vivo model for tumor-inhibition efficacy studies with 131I-cNGEGQQc. The tumor growth decreased significantly in mice receiving 131I-labeled peptide compared with the controls and the effect of 131I-labeled peptide can be blocked by unlabeled cNGEGQQc. Safety studies showed that 131I-cNGEGQQc was relatively safe for animals without significant toxicity. Our data suggest that 131I-cNGEGQQc has potential as a targeted radiotherapeutic agent for non-small-cell lung cancer.