PbSe nanocrystalline thin films have been prepared on glass and quartz substrates by chemical bath deposition method, using sodium selenosulfate, which acts both as a source of Se2- ions and a complexing agent, in the chemical bath. Effect of pH and temperature variation of the bath on grain size in the films is investigated; it is observed that the grain size increases with increase in pH and temperature. The films grow with typical rock salt structure of PbSe and the lattice parameter shows a slight increase with decrease in the grain size. Morphology of the grains is observed to be sensitive to their size. While the smaller grains are spherical, the larger nanoparticles appear to gradually transform from spherical to square platelets and cubes. Optical bandgaps (Eg) in the nanocrystalline films increase with decrease in grain size and have values larger than 0.28 eV of bulk PbSe. The observed blueshift in the films is expected to originate from quantum confinement in the nanograins. (c) 2007 The Electrochemical Society.