Rubber Elongation Factor (REF1) protein is located on the surface of rubber particles (RPs). As a RP-bound and hydrophobic protein, REF1 is suspected to be only partially eliminated by the water washing occurring during latex processing into raw natural rubber (NR) in the form of unsmoked rubber sheet (USS) and could thus affect raw NR properties. In this work, REF1 was identified as an abundant protein of raw NR and bio physical methods were used to describe the organization/structure of REF1 at the surface of RPs interacting with the lipid monolayer surrounding the poly-isoprene core. Therefore, an approach in Langmuir film was implemented to investigate the interactions between recombinant REF1 and synthetic phospholipids (POPC, POPG and POPA) by fluorescence (calcein-leakage measurements), ellipsometry, Brewster angle microscopy, and PM-IRRAS spectroscopy. REF1 was shown to interact differently depending on lipid headgroup type: no interaction with POPC, intermediate interactions with POPG and strong interactions associated to a conformational switch from a-helices to ß-sheets with POPA.