To explore the size effect on the yielding behavior of ultrathin superalloy sheets with different thicknesses and grain sizes, the experimental yield loci were obtained via uniaxial tensile and biaxial tensile tests under different loading ratios. The results indicated that the yield locus of ultrathin superalloy sheet shrink inward entirely with the increase of grain size, and the shape of yield locus is also changed from ellipse to square, indicating the grian size dependence of yield locus. In addition, the four typical macroscopic yield criteria were selected for comparative analysis, and results showed that the Yld2000-2d yield criterion keeps the best precision for describing the yielding behavior of ultrathin superalloy sheet. However, the prediction accuracy is degraded with the increase of grain size.