Abstract Free-standing diamond films with 1.68mm in polished thickness have been prepared by DC arc plasma jet CVD. By means of simply changing the placing orientation of diamond films along the laser transmission direction while testing, the through-thickness thermal conductivity (κ⊥) together with the in-plane (κ//) thermal conductivity of free-standing diamond films were measured by laser flash technique over a wide temperature range. Results show that the thermal conductivity κ⊥ and κ// of free-standing diamond films are up to 1916 and 1739Wm−1K−1 at room temperature, respectively, showing small anisotropy (9%), and following the relationship κ~T−n as temperature rises. The conductivity exhibits similar value compared to that of high-quality single crystal diamond above 500K for both through-thickness and in-plane directions of CVD diamond films. The effects of impurities and grain boundaries on thermal conductivity of diamond films with increasing temperature were discussed.