The influence of the local crystallographic orientation of the polycrystalline bottom platinum electrode on the crystallization of niobium pentoxide thin films during their rapid thermal annealing was investigated by X-ray diffraction, X-ray reflectivity and transmission electron microscopy. The Nb ₂O ₅ thin films under study were reactively sputtered in a mixed O ₂/Ar atmosphere and subsequently subjected to the annealing in argon atmosphere at temperatures ranging from 500 °C to 700 °C. The X-ray diffraction confirmed a transition from the amorphous niobium oxide to the crystalline orthorhombic Nb ₂O ₅ for temperatures between 500 °C and 600 °C. The X-ray reflectivity measurements showed that the crystallization process was accompanied by a continuous increase of the electron density in Nb ₂O ₅ and by a rapid increase of the surface roughness at 700 °C. It was further observed by transmission electron microscopy that Nb ₂O ₅ crystallizes selectively and that the crystalline domains of Nb ₂O ₅ possess a strong orientation relationship to the platinum from the bottom electrode. The orientation relationship (111)Pt ||(160)Nb ₂O ₅ was identified as the most beneficial one for crystallization of Nb ₂O ₅.