An experimental study of the copper-thiosulfate system in mild acidic (pH similar to 5) aqueous solutions, with respect to thin-film formation, was undertaken. Thin films of CuxS (1 less than or equal to x less than or equal to 2) were deposited by a simple electroless technique on glass or transparent polyester films, at 50 degrees C. Thin films were deposited from chemical baths in which the ratios of copper to thiosulfate were varied from 1:1 to 1:10. Thin films of different compositions (Cu2S, Cu1.8S, Cu1.4S and CuS) were prepared and then characterized for morphological, optical and electrical properties. The deposited films chemically close to Cu2S were found to be amorphous, while the CuS films were a mixture of both amorphous and polycrystalline phases. The optical spectra of the Cu2S films exhibited high transmission both in the visible region of the spectrum (beyond 600 nm) and throughout the near-infrared region (800 to 2500 nm), while CuS films were found to be highly absorptive throughout the near-infrared region, with peaked transmission in the visible region at about 560 nm. The sheet resistances of the films, determined by the standard four-probe measurements, were between 100 and 650 Ohm/square.