The formation of CuIn(S,Se)(2) thin films by thermal diffusion of sulfur (S) and selenium (Se) vapours into co-sputtered Cu-In alloy within a closed-space graphite container is reported. All films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), Four-point-probe and hot-probe measurements. Cu-In alloy films with composition varying from Cu-rich to In-rich were deposited. The synthesized In-rich films yielded CuIn,(S,Se), spinel compound which gradually transformed into a single phase CuIn(S,Se), as the him composition approached the Cu-rich region. The morphology of the CuIn,(S,Se), was found to differ from the stoichiometric and Cu-rich CuIn(S,Se), as observed from SEM. EDX composition analysis of the films showed a Cu/In ratio varying from 0.36 to 1.54 and a (S + Se)/Cu + In) varying from 0.97 to 1.32. The amount of S incorporated in the films was found to differ with changes in the composition. The resistivity of the films ranged between 10(-1) and 10(7) Ohm cm and it strongly followed the change in the alloy film composition.