The homogeneous coprecipitation (electroless method) technique has been utilized successfully to deposit Bi2S3-PbS alloy thin films on glass substrates. Characterization of such films have been carried out using X-ray diffraction, scanning electron microscopy (SEM) and resistivity studies. It has been observed that powders and thin films deposited by this method behave differently. The crystal structure remains distorted orthorhombic although the lattice constants change upon alloying. Both substitutional and interstitial replacement of cations and anions take place in this system in the case of powders as well as thin films. SEM and resistivity studies corroborate these above observations.