An effective approach to stabilize emulsions is to increase the rigidity of oil–water (O/W) interfacial films by adsorbing molecular assemblies such as lamellar phases around the emulsion particles. In this study, we aimed to analyze the structure of a lamellar phase adsorbed at an O/W interface and to clarify the effect of the structure and physicochemical properties of the lamellar phase on the dispersion stability of emulsions. The adsorption of the lamellar phase at the O/W interface of the emulsions was confirmed by freeze-fracture transmission electron microscopy of O/W emulsions prepared by diluting and dispersing gels formed with polyglycerol fatty acid esters, water, and cetyl isooctanoate (CIO). The structure of the lamellar phase adsorbed at the O/W interface was analyzed in detail through small-angle X-ray scattering measurement and indirect Fourier transform analysis. The lamellar phase adsorbed at the O/W interface was shown to have an interdigitated structure with low CIO content, whereas it changed to a non-interdigitated structure with increasing CIO content. Furthermore, the adsorbed lamellar phases with interdigitated structures and high rigidity provide the emulsion with higher dispersion stability.