Creep rupture tests were performed for a die-cast Mg-Al-Mn alloy, AM50, at temperatures between 423 and 498K under stresses between 30 and 120 MPa, and the creep rupture lives were evaluated by using the Larson-Miller parameter (LMP). The value of LMP is uniquely described by the logarithm of the applied stress for the alloy, when the Larson-Miller constant is chosen as fifteen rather than twenty. The Larson-Miller constant depends predominantly on the morphology of intermetallic phases in microstructure for magnesium alloys. (C) 2011 Elsevier B.V. All rights reserved.