Abstract: Lead sulfide （PbS） nanoparticles coatal by dialkyldithiophosphate （DDP） were synthesized with the method of ion modification. The nanoparticles were characterized by infrared spectroscopy （IR）, X-ray diffraction （XRD）, transmission electron microscopy （TEM） and X-ray photoelectron spectroscopy（XPS）. Results indicated that the DDP molecules coated around the PbS nanocrystallines which made the PbS nanoparticles have good dispersion capacity in organic solvents and are protected from oxidation in air.