Pb1-xSnxS nanopowder with different Sn concentrations (x = 0.02, 0.05, 0.10, 0.20, 0.50 and 1.00) were synthesized by chemical precipitation route under N2 atmosphere. The samples were characterized by X-ray diffraction(XRD), UV-vis absorption spectra and photoluminescence (PL) spectra. The XRD results show that the samples with 0 ≤ x ≤ 0.2 have cubic (fcc) structure with diameter in the 12.8–24 nm range. The sample with x = 0.5 has orthorhombic structure with a diameter of 9.2 nm. The band gap (or absorption edge) of PbS exhibits a large blue shift when the crystallite size is reduced to nanometer scale, from 0.4 eV in bulk samples to 1.8 eV in nanosize samples, which can be related to large Bohr excitonic radius of PbS nanoparticles. PL emission spectra of Pb1-xSnxS in red region excited at 315 nm, for x = 0 showed three broad peaks located at 776.5 nm, 809 nm and 826 nm which due to the defect densities and for x = 0.02, 0.05, 0.10 there are two relatively strong emission peaks located at 786 nm and 823 nm which can be related to transition from sulfur vacancy level and Sn+2 ion level respectively.