Nanocrystalline PbS thin films have been deposited on glass substrates by Chemical Bath Deposition (CBD) technique using lead acetate ,KoH, thiourea and T.E.A. The films were btained in a reaction bath at times of (15 ,30 ,45 ,60 and 90)min. Structure and surface morphology of thin films were characterized by X-ray diffraction and scanning electron microscopy (SEM). XRD indicates that the films have cubic structure. The crystallite size of the films were found to vary from (4.9 to 11.3 nm).The band gaps of the nanocrystalline PbS were determined from UV-Vis spectrophotometer and were found to be in the range( 1.72 -2.4 eV).