Abstarct: The purpose of this study is a theoretical and experimental study of molybdenum trioxide (MoO3) in the orthorhombic phase (α-MoO3). In the experimental part of this thesis, undoped and iron (Fe) doped molybdenum oxide samples were synthesized using the facile and cost-effective technique of hydrothermal. The structural, optical, elemental composition and morphological properties of the synthesized samples were studied. The effects of Fe doping, at different weight percentages, were investigated on the MoO3 properties. XRD pattern analysis of the undoped and all Fe-doped samples indicates the growth of molybdenum oxide in the orthorhombic phase and Raman spectroscopy confirmed the XRD results. In the Fe-doped samples bandgap decreased compared to the undoped sample. FESEM images of the samples are another indication of the formation of α-MoO3 nanobelts with a laxyered structure. With Fe dopant increment, obvious changes in the morphology of this material were observed. In the theoretical part of this thesis, the electronic and structural properties of the undoped and Fe-doped α-MoO3 with and without oxygen vacancy have been studied using density functional theory (DFT). The calculations were performed using WIEN2k software baxsed on the full-potential linearized augmented plane wave (FP-LAPW) method within GGA approximation. The obtained results show an indirect bandgap with a value of 2.24 eV in the undoped MoO3 that is in good agreement with other reports. Also, this value is close to the amount of bandgap calculated in the experimental part. Different concentrations of impurity and oxygen vacancy lead to a significant decrease in the amount of bandgap. The plots of the density of states show changes in the magnetic properties of the material in the presence of impurity.