X-ray diffraction, scanning electron microscopy, compositional analysis and transmission measurements are performed on InSe thin films grown by thermal evaporation at different substrate and annealing temperatures of 150-250 degrees C and 100-200 degrees C, respectively. An analysis of structural measurements indicates that there exist three phases of In-Se system like InSe, In2Se3 and In6Se7 in the same film at low-substrate temperature, but at high-substrate temperatures, In2Se3 phase was absent. The composition of InSe films changed significantly with substrate temperature and slightly with annealing temperature because of re-evaporation of selenium. The transmission measurements were carried out at room temperature over the spectral range 0.5 to 2.5 mu m. As a result of optical energy gap studies, the direct energy band gap was found to be in between 1.21 and 1.38 eV depending on substrate and annealing temperatures.