Mn-doped PbSnanocrystalline thin films of three different dopant concentrations of 1 wt.%, 1.5 wt.% and 2 wt.% Mn were deposited onto glass substrates at 313K by Chemical Bath Deposition Method (CBD) using lead acetate and thiourea as precursors with Manganese acetate as dopant precurser. The as prepared thin films were characterized by using X-ray diffraction (XRD), Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM) and Energy Dispersive X-ray (EDAX). Analysis of energy dispersive X-ray confirmed the presence of Pb, Mn and S elements. The particle size of the prepared nanoparticles decrease with the increase of dopant concentrations.For 0 wt.%, 1 wt.%, 1.5 wt.% and 2 wt.% Mn dopant concentrations, the average crystallite sizes were found to be 21 nm, 17 nm, 14 nm and 11 nm respectively. The decrease in crystallite size with the increase in dopant concentrations may be due to the replacement of larger radius lead ions by the smaller radius Mn ions.