Hybrid assemblies composed of phospholipids and amphiphilic polymers have been investigated previously as a biomimetic model of biological cells. However, these studies focused on the functions of polymers in a sea of membrane lipids. Here, we prepared a highly stable peptide-lipid hybrid vesicle from a combination of an amphiphilic polypeptide and the phospholipid, 1,2-dimyristoyl-sn-glycero-3-phospho-choline, with a mixing molar ratio of 1:1. The phase-separated structure of the hybrid vesicle was demonstrated by fluorescence resonance energy transfer analysis. The lipid domain of the hybrid vesicle had a phase-transition temperature of 38 degrees C and allowed the permeation of a hydrophilic molecule, fluorescein isothiocyanate-labeled polyethylene glycol (M-w: 2000), above 38 degrees C. The designed peptide-lipid hybrid vesicle and a "lipidic gate" are a promising tool for smart drug delivery.