Amphiphilic Janus gold nanoparticles(GNPs) are prospected to encapsulate drug molecules in cancer therapy and to serve as heterogeneous catalysts at oil/water interfaces, where Janus GNPs with different sizes are required. In this work, multiple-sized precursor GNPs were synthesized by seeded growth method protected with tris(hydroxymethyl)phosphine oxide(THPO) ligand molecule, and a ligand exchange reaction with triphenylphosphine(PPh3) at the toluene/water interface was employed to prepare amphiphilic Janus GNPs. UV-vis and transmission electron microscopy(TEM) analyses indicate that the as-prepared GNPs are nanocrystals with average diameters of 2.3 nm, 9.5 nm, 16.1 nm and 18.8 nm, respectively. Contact angle, Raman and X-ray photonic spectroscopy(XPS) analyses reveal that the selfassembled GNP films exhibit hydrophilic on one side and hydrophobic on another, owing to the adsorption of hydrophilic ligands(THPO and THP) and a similar amount of hydrophobic ligands(PPh3 and PPh3O).Angle-resolved XPS analysis further demonstrates that the individual GNPs actually possess hydrophilic and hydrophobic compartments on the surface, which regularly packed by supramolecular interactions at toluene/water interface to form the self-assembled GNP films. Amphiphilic Janus gold nanoparticles (GNPs) are prospected to encapsulate drug molecules in cancer therapy and to serve as heterogeneous catalysts at oil / water interfaces, where Janus GNPs with different sizes are required. In this work, multiple-sized precursor GNPs were synthesized by seeded growth method protected with tris (hydroxymethyl) phosphine oxide (THPO) ligand molecule, and a ligand exchange reaction with triphenylphosphine (PPh3) at the toluene / water interface was employed to prepare amphiphilic Janus GNPs. Analyses indicate that the as-prepared GNPs are nanocrystals with average diameters of 2.3 nm, 9.5 nm, 16.1 nm and 18.8 nm, respectively. Contact angle, Raman and X-ray photonic spectroscopy (XPS) analyzes reveal that the selfassembled GNP film exhibit hydrophilic on one side and hydrophobic on another, due to the adsorption of hydrophilic ligands (THPO and THP) and a similar amount of hydrophobic ligands (PPh3 and PPh3O) .ngl e-resolved XPS analysis further demonstrated that the individual GNPs actually possess hydrophilic and hydrophobic compartments on the surface, which regularly packed by supramolecular interactions at toluene / water interface to form the self-assembled GNPs.