Interleukin-4 receptor α (IL-4Rα) is highly expressed on the surface of various human solid tumors including head and neck squamous cell carcinoma (HNSCC). We designed a novel IL-4Rα-lytic hybrid peptide composed of a binding peptide to IL-4Rα and a cell-lytic peptide. In the present study, we evaluated the antitumor activity of the IL-4Rα-lytic hybrid peptide as a novel molecular-targeted therapy in HNSCC. Immunoblot analysis revealed that IL-4Rα was expressed in all tested HNSCC cell lines (HSC-2, HSC-3, HSC-4, Ca9-22 and OSC-19), but not in a human normal keratinocyte (HaCaT) cell line. Immunohistochemical expression levels of IL-4Rα in HNSCC tissues were higher compared to those in normal epithelial tissue. The IL-4Rα-lytic hybrid peptide showed cytotoxic activity in all five cancer cell lines with a concentration that killed 50% of all cells (IC50) as low as 10 µM. HaCaT cells were less sensitive to this peptide with an IC50 of >30 µM. In addition, intratumoral administration of IL-4Rα-lytic hybrid peptide significantly inhibited tumor growth in a xenograft model of human HNSCC in vivo. These results indicate that the IL-4Rα-lytic hybrid peptide may serve as a potent agent to provide a novel therapy for patients with HNSCC.