Abstract: In this paper, the effect of annealing temperature on Indium antimonide (InSb) thin films has been studied. It is proved that the increase in annealing temperature enhances the crystallinity of the InSb thin film. Thin films of InSb have been deposited on silicon and glass substrates by RF sputtering, then vacuum-annealed at 150, 300, 390 and 450 ⁰C. Differential scanning calorimeter (DSC) analysis indicates that InSb thin film crystallizes at 389 ⁰C or above. X-ray diffraction (XRD) results show peaks at (111), (220) and (311) planes, which indicates the formation of crystalline grains. Fourier transform infrared (FTIR) spectroscopy indicates the decrease of optical transmittance upon increasing the annealing temperature, the analysis shows that InSb thin films have bandgaps between 0.233 and 0.241 e.v.