Radiation therapy is one of the most common treatments for cancer. However, enhancing tumors' radiation sensitivity and overcoming tolerance remain a challenge. Previous studies have shown that the Ras signaling pathway directly influences tumor radiation sensitivity. Herein, we designed a series of Ras-targeting stabilized peptides, with satisfactory binding affinity (KD = 0.13 μM with HRas) and good cellular uptake. Peptide H5 inhibited downstream phosphorylation of ERK and increased radio-sensitivity in HeLa cells, resulting in significantly reduced clonogenic survival. The stabilized peptides, designed with an N-terminal nucleation strategy, acted as potential radio-sensitizers and broadened the applications of this kind of molecule. This is the first report of using stabilized peptides as radio-sensitizers, broadening the applications of this kind of molecule.