The oxidation behavior of K38 alloy with 0, 0.05, 0.1, 0.5wt% yttrium concentrations has been investigated during exposures in air at 1173K for 100 hours. The results indicated that Cr2O3 and TiO2 scale mainly formed on the surface of the alloy without yttrium. Yttrium addition promoted the selective oxidation of aluminum and reduced the internal oxidation. The alloy with 0.1 wt.% yttrium addition exhibits excellent oxidation behavior among the four types of the alloys for its decreasing the oxidation rate and forming more continuous and compact Al2O3 scales. Yttrium-rich phase formed in the alloy with 0.5wt.% yttrium, result in a negative effect on the oxidation resistance of cast alloys.