Indium sulfide thin films were deposited onto indium-doped tin-oxide substrates with different deposition times (60 h, 63 h, 66 h, and 69 h) at room temperature by using a chemical bath deposition method to obtain new structures for solar cells. The film obtained at 60 h was annealed at 400 degrees C for 1 h in nitrogen media. The crystallographic structure of the films was observed via the X-ray diffraction pattern while the size and shape of the grains were characterized by scanning electron microscopy. Moreover, the optical transmission spectra of the films were obtained at room temperature in the wavelength range of 300-1100 nm. After the films were annealed, the optical transmission decreased from 52% to 26% at a wavelength of 550 nm. With increasing film thickness and grain size, the direct and indirect optical band gap of the InS films decreased from 2.31 eV to 2.19 eV and from 1.89 eV to 1.75 eV, respectively. The refractive index, extinction coefficient, and dielectric constant of the films were determined. The sheet resistivity of the films decreased from 33 Omega cm to 28 Omega cm with increasing grain size.