One potent way of improving scale adhesion of nickel aluminide or platinum aluminide coatings on Ni-based superalloys is to incorporate a small amount of “reactive element” such as Y, Hf, Zr, etc. The challenge in the actual fabricating process is how to control the reactive element at a desired level with uniform distribution in the coating in order to manifest its beneficial effect. In the present study, the Hf-modified aluminide coatings were synthesized by a pack cementation process. Detailed coating microstructure characterization was conducted using X-ray diffraction (XRD), scanning electron microscopy equipped with energy dispersive spectroscopy (SEM-EDS), and electron probe microanalysis (EPMA). The oxidation behavior of these Hf-modified aluminide coatings were investigated and compared with similar coatings without Hf. Also, the coating oxidation performance was compared with aluminide coatings made by chemical vapor deposition (CVD) which have been extensively characterized and tested.