The silver salts of fatty acids were thermally decomposed at 250 degrees C in an atmosphere of nitrogen to form silver nanoparticles with a size of 5 nm. The particles suspended in toluene put on a hydrophilic surface of the plasma-polymerized film of osmium tetraoxide and on a water surface to form a two-dimensional array. The nanoparticles repelled each other with a distance of 2.8-3.5 nm depending on the length of the alkyl chain. The surface pressure-area isotherms were measured to confirm the condensation mechanism of two-dimensional arrangement of nano-particles surrounded by alkyl moieties.