Magnesium alloy GW103 samples were heat treated to different ageing conditions and then shot peened using process parameters that deliver optimized high cycle fatigue (HCF) life. Significant HCF life improvements were observed in all samples, with a peak-aged sample showing the biggest increase. In order to simulate the effect and evolution of residual stresses during low cycle fatigue (LCF), a Finite Element (FE) model was employed, taking into account both the shot-peening-induced plastic strains and the influence of hardening on subsequent deformation. Experimental and modelling results offer a basis for explaining the observed fatigue performance improvement due to shot peening. (C) 2012 Elsevier Ltd. All rights reserved.