The structures of thin V(25 nm)/SiO$_2$(001), V(25 nm)/MgO(100), V(25 nm)/Al$_2$O$_3$(0001), V(25 nm)/SrTiO$_3$(100) films on different monocrystalline substrates are studied in the initial state and under annealing up to 600°C in vacuum of 10$^{-3}$ Pa. Preferred orientation of grains along the [110] direction in the films on SrTiO$_3$(100) substrate with coherent-scattering area size of about 11 nm and lattice parameter of 3.024 Å that corresponds to the bulk state is revealed by using synchrotron radiation (RIKEN SPring-8 Center). The near-surface oxidation degree in the initial state is determined by the long-range influence of the transition-layer structure at the ‘thin film–substrate’ interface. This structure depends on both the crystal-structures’ types of thin film and substrate and the degree of mismatch between them. Oxidation is inhibited when the transition layer is amorphous. Oxidation at the initial stages of annealing also depends on initial structure of vanadium film. When the axis of texture is normal to the outer surface, longitudinal channels caused by grain boundaries and triple boundaries’ junctions become dominant pathways for accelerated diffusion of oxygen. When the temperature exceeds the threshold value of 350°C, the process of transformation of b.c.c. vanadium-crystal lattice into monoclinic one starts. A possibility of the ordered substitutional solid solution of oxygen atoms in vanadium lattice is discussed.