The deformation behaviors of rectangular-parallelepiped micropillars fabricated from [0011-oriented Nibased superalloys with negative and positive lattice misfits, respectively, were investigated with respect to the specimen size. The yield stresses of the larger specimens (side length L > -2 mu m) of both considered alloy types were found to be nearly independent of the size, while the smaller specimens (L <-2 mu m) exhibited "smaller is stronger" and "smaller is (slightly) weaker" trends for negative and positive lattice misfits, respectively. The internal stresses calculated based on the micro-elasticity theory revealed that the internal shear stress fields of the micropillars varied with their sizes. The size dependence of the calculated internal shear stress distribution agreed fairly well with the experimentally determined size dependence of the yield stress, indicating that the distribution of the internal misfit stress significantly contributed to the size-dependent yield stress of the smaller micropillars. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.