The authors report on the experimental investigation of the thermal conductivity of nitrogenated ultrananocrystalline diamond (UNCD) films on silicon. For better accuracy, the thermal conductivity was measured by using two different approaches: the 3ω method and transient “hot disk” technique. The temperature dependence of the thermal conductivity of the nitrogenated UNCD films was compared to that of undoped UNCD films and microcrystalline diamond (MCD) films on silicon. It was shown that the temperature dependence of the thermal conductivity of UNCD films, which is substantially different from that for MCD films, can be adequately described by the phonon-hopping model. The room-temperature thermal conductivity of UNCD is 8.6–16.6 W/m K and decreases with the addition of nitrogen. The obtained results shed light on the nature of thermal conduction in partially disordered nanostructured materials and can be used for estimating the thermal resistance of doped UNCD films.