Ru coating prior to aluminizing is one of the effective methods to reduce the harmful intermediate layer that forms under the coating (SRZ) on a 4(th) generation Ni-base SC superalloy. This study examined the short-term isothermal oxidation behavior of this Ru-modified coating at 1373 K in air. Surface observation by SEM showed that the scale becomes flat and uniform in comparison to simple aluminide coating. XRD and cross-sectional analysis results also showed that phase transformation from beta-NiAl to gamma'-Ni3Al seldom occurs in the Ru-modified coating layer leading to the prevention of local oxidation.