CdS1−xSex thin films were deposited on Corning glass substrates at 75°C by chemical bath deposition (CBD) varying the composition “x” from 0 to 1 at a constant deposition time of 120min. The composition of the films was adjusted by modifying the concentration as well as the ratio of the precursors. The morphological, compositional, structural and optical properties of the films were analyzed using several techniques such as Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X-ray Diffraction (XRD), UV–Vis Spectroscopy (UV–Vis) and Photoluminescence (PL). The films grow as layers following the ion by ion mechanism, the density of the films decreases with x. Films are constituted by clusters (100–600nm in diameter) of semispherical particles with sizes fluctuating from 10 to 20nm. For x⩾0.5 the particles are well-arranged in a “worm-like” structure. All the films are polycrystalline, to x=0 (CdS) the cubic phase is present, the increase of composition promotes the formation of hexagonal phase or a mixture of both cubic and hexagonal phases. Preferential orientation in the (100) or (002) plane is observed. The crystal size decreases from 20 to 6nm when x is increased. The optical properties can be easily tuned by adjusting the composition. Optical absorption analysis shows that the band gap (Eg) value shifts to red in function of x (from 2.47 to 1.99eV). Photoluminescence signal changes as “x” varies showing a regular behavior from x=0 (CdS) to x=1 (CdSe). The main band, attributed to cadmium vacancies (VCd), is shifted according to x. Improvement of the PL signal has been reached after annealing with CdCl2 salt.