Indium sulfide (In sub(2)S sub(3)) thin films were deposited on polyethylene naphthalate (PEN) by chemical bath deposition (CBD). The materials were characterized by ultraviolet (UV)-visible spectroscopy, x-ray photoelectron spectroscopy (XPS), energy-dispersive x-ray spectroscopy (EDX), scanning electron microscopy (SEM), and x-ray diffraction (XRD) to investigate the influence of the polymeric substrate on the resulting thin In sub(2)S sub(3). The films showed polycrystalline (cubic and tetragonal) structure. A reduction of the ordering of the polymeric chains at the surface of the PEN was also observed, demonstrated by the appearance of two infrared bands at 1094 cm super(-1) and 1266 cm super(-1). Presence of oxygen during the early stages of In sub(2)S sub(3) growth was also identified. We propose a reaction mechanism for both the equilibrium and nucleation stages. These results demonstrate that In sub(2)S sub(3) can be deposited at room temperature on a flexible substrate.