Lead sulfide (PbS) and Au-PbS core-shell nanoparticles were successfully synthesized using the sonochemical method at room temperature. The morphology of the synthesized particles was characterized by FESEM and TEM images. Pure fcc phase of PbS and Au crystal structures was examined and confirmed by XRD patterns. The quantum confinement effect plays a crucial role in blue-shifting the absorption edge and the band gap energy of both solid PbS nanoparticles and a thin spherical PbS shell toward shorter wavelength region in comparison to those of PbS bulk. Due to the high refractive index of PbS shell, Surface Plasmon Resonance (SPR) peak of Au nanocores is significantly red-shifted by roughly 80 nm toward the longer wavelength region. More sophisticate experimental data and some adequate theoretical models are needed to fully explain the matters.