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High temperature oxidation behaviors of cast K317 and K325 alloy at 900°C and 1000°C in air environment are contrastively investigated by TGA, XRD and SEM (EDS). The results show that K317 alloy has a superior oxidation resistance compared with K325 alloy. The kinetic curves of two alloys oxidized at 900°C for 100 h obey the parabolic rate law while those at 1000°C obey sectionally the parabolic rate law. The oxide structure of K317, from the top surface down to the base material, consists of NiO-TiO₂-NiCr₂O₄ composite oxide, Cr₂O₃ oxide dense band and Al₂O₃ internal oxide. In comparison, internal oxidation is not observed in K325 alloy whose oxide layer is composed by two oxide layers: NiO-NiCr₂O₄-Nb₂O₅ composite oxide and Cr₂O₃ oxide layer. Serious MoO₃ volatilization and oxide spallation take place in K325 alloy after the oxidation at 1000°C for 100h. In addition, the adhesion property of K325 alloy is worse than that of K317 alloy due to the occurrence of the micro-voids on the oxide layer/substrate interface.