The uniform nanoparticles PbS with diameters about 13 nm could be synthesized by Desulfotomaculum sp. under mild condition. The effects of the processing variables such as pH and temperature were investigated. The obtained products were in detailed by means of transmission electron microscopy (TEM) and X-ray diffraction (XRD), respectively. The results revealed that the PbS crystallites were identical in structure, shape and size under different temperatures while their morphology changed from rod to spheroidal with pH increasing. In the biological synthetic process for PbS nanoparticles, Desulfotomaculum sp. can use sulfate as a terminal electron acceptor to produce sulfide which acts as the source of sulfur for the formation of PbS nanoparticles.