Abstract: MoO3 films were deposited on glass substrates by electron beam evaporation method. X-ray diffraction patterns revealed that the prepared samples presented orthorhombic structure with preferred orientation of . As substrate temperature increased, the grain size increases firstly then decreases, but increases once more after annealing. Moreover, the diffraction peak of (040) plane shifts to lower angle monotonically with increased substrate temperature. Scanning electron microscope images show needle-like grains and their size becomes more uniform after annealing. With increased subsutrate temperature, the sample optical absorption edge in ultraviolet-visible spectra shift to longer wavelength and the transmittance also decreases. On the other hand, the optical gap reduces from 2.93 eV to 2.59 eV when substrate temperature increases from 100 ℃ to 300 ℃, and even reduces to 2.46 eV after air annealing under 500 ℃.