Traditionally, Argon (Ar) is used as a working gas to deposit MgF2 thin films in ionbeam assisted deposition (IAD) process. It improves the quality of the films, but cannot reduce the loss of F- ions during the process which also results in other impurities appearing in MgF2 thin films. The contaminants in MgF2 film such as C, O and Ar atoms are identified by X-ray photoelectron spectroscopy (XPS). In this study, sulfur hexafluoride (SF6) was chosen as a working gas in which more F– ions were created from the dissociation of SF6 in the IAD process in order to increase the content of F and eliminate the contamination. In our knowledge, very few reports have been published on IAD used SF6 as a working gas in optical coating process at around room temperature. Deposition of unwanted sulfur atoms was the concern when SF6 was used in the IAD process, however, no sulfur was observed in XPS spectra. The XPS spectra of Mg 2p, O 1s and F 1s were decomposed and analyzed with some Gaussian sub-peaks. The transmission spectra of films were measured in UV and visible ranges. The water absorption phenomena in the films were also measured by Fourier Transform Infrared (FTIR) spectrometer. Compared to the films fabricated by other methods, using SF6 as a working gas in IAD is a good choice to deposit MgF2 films.