A cheap and more environmentally friendly method for the synthesis of high quality PbS nanoparticles in olive oil at 60 °C has been developed. Carefully controlling the conditions of reactions leads to PbS nanoparticles with well-defined sizes, and band gaps between 1.72 and 0.88 eV. The nanoparticles were characterized by XRD, HRTEM, NIR absorption spectroscopy, X-ray photoelectron spectroscopy (XPS) and a fluorescence lifetime experiment based on the time-correlated single photon counting (TCSPC) technique. Photoelectrochemical study carried out by steady-state current-voltage measurements of self-assembled PbS nanoparticles on ZnO-SnO2 electrodes in 1 M Na2SO3 electrolyte solution showed that as-prepared PbS nanoparticles were photochemically active. © The Royal Society of Chemistry 2010.