The ability of a number of amphiphilic di- and triblock copolymers bearing short blocks of repeating lipid-mimetic units to sterically stabilize egg-phosphatidylcholine (EPC) liposomes has been studied by means of light scattering, cryogenic transmission electron microscopy (cryo-TEM), and fluorescence spectroscopy. The hydrophobic blocks contain 1-4 lipid-mimetic units, whereas the hydrophilic blocks consist of poly(ethylene glycol) (PEG) of average molecular weights close to 5000 Da. The effect of the chain architecture was investigated as well. The structural changes and membrane permeability were studied as a function of the amount of the incorporated copolymer. The structural investigations, performed by means of cryo-TEM, revealed that the maximum amount of the copolymer that can be incorporated in the EPC membrane without affecting the liposome integrity increases with increasing number of the lipid-mimetic anchors per single copolymer chain. This helps the formation of a dense and thick PEG protective layer which, in turn, is expected to enhance the liposome longevity. At the same time, the membrane permeability, investigated using a hydrophilic dye as a probe, was only slightly affected by the incorporation of the copolymers. The structural changes and membrane permeability are discussed in light of the shape of the macromolecules and the phase propensity of the steric stabilizers.