We investigated the atomic and electronic properties of (100) stacking fault (SF) in undoped and La-doped BaSnO3 by first-principles calculations. It was found that 1/2[111] (100) SF is energetically favorable when Ba atoms occupy the interface while 1/2 (100) [101] SF becomes the most stable when the SF interface is occupied by Sn atoms. SF influences the distribution of La dopant and the electric properties of the system. In the presence of SF, electronic states near the Fermi level decrease and the bandgap expands by about 0.6 eV. Our results suggest that SF is one of the possible origins for the performance degradation. (C) 2018 Elsevier B.V. All rights reserved.