The isothermal oxidation of two types of Ni-based alloy,alloys800H and HR-120 was investigated in this study. The alloyunderwentan isothermal oxidation test at 950ºCfor 150 hours of exposure. Oxdisedalloys were tested using oxidation kineticsmethods,phase analysis using X-ray diffraction (XRD) and oxide morphology using scanning electron microscopy (SEM) techniques. Oxidation kinetics were determinedbased on the weight change per surface area of the oxidised alloy over a 30-hour interval. As a result, both alloys displayeda pattern of weight gain as the exposure period increased. Both alloys have followed a parabolic rate law,indicating a controlled kineticsof oxide scale diffusion. XRD analysis showedthat the main Cr-containing oxide has formed on the surface of the alloy with the addition of Ti oxide for the 800H alloy and Nb oxide for the HR-120 alloy due to the different alloying element content of the two alloys. Oxide surface morphology records the uniform oxide scale that forms on the surface of the alloy.