Dendron lipids designed to consist of amine-terminated polyamidoamine G1 dendron and two octadecyl chains were used for: the preparation of pH-responsive molecular assemblies having phase structures that are changed through their dynamic molecular shape. The dendron lipid contains two primary amines and two tertiary amines in the dendron moiety, changing its charged state in the pH region between pH 10 and pH 4. The assemblies were shown to take a vesicle structure at neutral and alkaline pHs, but their structure changed to a micelle-like structure below pH 6.4. Because this pH region corresponds to one in which tertiary amines of the dendron lipid became protonated, protonation of tertiary amines in addition to primary amines in the dendron moiety might affect its dynamic molecular shape, resulting in a sharp pH response of the assemblies. The assemblies :tended to form aggregates when taking on a vesicle form with a gel phase, but incorporation of a poly(ethylene glycol) lipid provided,dendron lipid vesicles with both sharp pH response and high colloidal stability. The poly(ethylene glycol)-incorporated dendron lipid vesicles tightly retained ovalbumin molecules in their internal aqueous space but released them almost completely at pH 6.0. In addition, the vesicles were shown to achieve efficient ovalbumin delivery into cytosol of DC2.4 cells (manse dendritic cell line) after internalization through endocytosis.