Niobium-pentoxide films with thicknesses of 100 nm to 1 mum were deposited by both DC and mid-frequency (MF) magnetron sputtering using a dual magnetron (TwinMag((R))) configuration. Stress measurements were performed by determining the substrate curvature before and after deposition for various process parameters. By varying the argon or oxygen partial pressure, it could be shown that a minimization of the undesired compressive stress, caused by the particle bombardment, is attainable. It was found that the limits for achieving this strongly depend on the applied process (MF or DC) as well as on the target state (oxide or transition mode). The films were characterized using SEM, AFM, vibrating reed, EPMA, and XRD yielding information concerning morphology, stoichiometry, phase, and surface roughness. Furthermore, ellipsometric measurements allowed the determination of the film thicknesses and the refractive indices (n(550 nm) = 2.4) which turned out to be highly correlated to the stress values.