Monodisperse lead selenide nanoparticles have been successfully prepared via a sonochemical route from an aqueous solution of lead acetate and sodium selenosulfate in the presence of complexing agents under ambient air. It was found that when trisodium citrate was used as the complexing agent, the product was spherical nanoparticles with an average size of ca. 8 nm. If potassium nitrilotriacetate was used, the product consisted of rectangles with an average size of ca. 25 nm. The products were characterized by powder X-ray diffraction, transmission electron microscopy, selected area electron diffraction, and X-ray photoelectron spectroscopy. A probable mechanism for the sonochemical formation of PbSe was proposed. Several factors that affected the nature and morphology of the products were also discussed such as the pH value, the complexing agents, and the intensity of the ultrasound irradiation.