Nanoliposomes are widely used for drug delivery in the human body. Cell-penetrating peptides are amphiphilic peptides inserting in the lipid bilayer of these lipid vesicles to induce the fusion with target cells. Separation by size exclusion chromatography coupled with the analysis by light scattering detectors provides both the hydrodynamic radius and the radius of gyration of all the liposomes in a sample. In this paper, the influence of the insertion of a cationic peptide, K2LA12, on the size and shape of anionic liposomes has been studied by this approach. The results obtained highlighted an increase in size and a slight deformation of the lipid vesicles depending on the concentration of peptides incorporated into the lipid bilayers.