The Ultra-High-Vacuum (UHV) arc technology was proposed as an alternative for depositing thin superconducting films of pure niobium on the internal surfaces of RF cavities for particle accelerators. The paper describes status of research on the deposition of such films for the RF accelerating cavities. UHV arc-based devices, equipped with planar- or cylindrical-cathodes, are described. The main results of experiments and some characteristics of the arc-deposited thin Nb-films, as well as results obtained recently with the formation of such films, are also presented. The critical temperature Tc of the deposited Nb-films appeared to be very close to that of pure bulk niobium (Tc=9.26 K) and the transition to the superconducting state was very narrow. The deposited Nb-films had higher residual resistivity ratio (RRR) values (up to 80) and larger grains sizes, as compared with those sputtered at the same temperature. The …