Experiments on convective heat transfer from a rotating disk with fins, which are arranged along radial direction, are performed to know the heat transfer characteristics for designing the ECB retarder. Heat transfer coefficients at three different positions along the longitudinal direction of the fin are evaluated from temperature distribution obtained by thermocouples inserted in the fin. The result shows that the heat transfer coefficient at each position is much higher than that for the rotating disk without fin, and varies complexly with fin angle. The heat transfer enhancement by arranging fins is marked especially at low rotating speed condition, since turbulent flow heat transfer exists over almost the entire surface even at such condition, in which laminar flow heat transfer appears in the case of the rotating disk without fins. Finally the fin array which has the highest heat removal performance in the disks tested is shown.