By using a small-angle X-ray scattering technique, we have studied the structural properties of ganglioside/dipalmitoylphosphatidylcholine (DPPC) mixture in solutions. We have obtained the following evidences. A minor presence of ganglioside in the mixture strongly induces a structural change from a multilamellar vesicle to a unilamellar vesicle. The increase of ganglioside molar fraction in the mixture tends to stabilize and prevent the deformation of the vesicle structures against temperature elevation from 10 degreesC to 65 degreesC Combined with our previous results that the elevation of temperature induces the dehydration and bending of the ganglioside oligosaccharide chains, the present results suggest that ganglioside molecules are mostly located at the external side of the ganglioside/DPPC vesicle to reduce the radius of the vesicle and that in the temperature elevation process the bendings of the ganglioside sugar heads compete with chain-melting of the hydrophobic region of the vesicle to suppress a deformation of its structure.