We have investigated the migration of La3+ and Sr2+ by an A-site vacancy (V-A) mechanism in La1-xSrxMnO3 (LSMO). Ab initio calculations determine migration barriers of 2.96 eV and 2.42 eV, for La3+ and Sr2+, respectively, and that repulsion between Sr2+ and V-A is well-described by a screened electrostatic potential of the form E = 2.8 exp(-0.2r)/r eV, (r being separation in angstrom). Using these results to parameterize kinetic Monte Carlo (KMC) and analytical calculations for diffusion coefficients we find good agreement with experiment observations of A-site diffusivity in other perovskites. We use these results to consider the tendency for Sr2+ to kinetically demix. (C) 2013 The Electrochemical Society. All rights reserved.