Phenolics represent a large family of secondary metabolites, ubiquitous in the plant kingdom and highly diversified. Although under native form they are effective antioxidants, their hydrophilic nature may be sometimes prejudicial to their antioxidant efficacy. Indeed, in complex systems such as emulsions, membranes, and living cells, it is generally considered advantageous for antioxidants to exhibit surface-active properties. One strategy to obtain surface-active phenolics consists in their association via covalent bond with a lipophilic moiety to design a new class of molecule called “phenolipids”. As tailor-made new bioactive molecules, the phenolipids have proved to be a promising way to enhance their natural antioxidant property. This grafted lipophilic domain kinetically modulated the ability of the phenolipid to interact and cross cell membranes. Despite the evidence supporting a relationship between phenolipid's alkyl chain length and their interaction/affinity with membrane bilayer, such a relationship has not been directly visualized. In this study, the membrane interactions of rosmarinic acid, considered as one of the most efficient antioxidant, and its corresponding alkyl esters have been examined via small angle x-ray (SAXS) diffraction approach in model membrane liposomes and correlate with the overall peroxidation of the membrane.