Nano-alumina reinforced AS41 magnesium alloy matrix composites with 2wt% and 5wt% Al2O3 were fabricated by combined stir casting and ultrasonic processing in order to distribute the nano-alumina particles uniformly in the melt. Indentation creep tests were performed on the nano-composites and the as cast AS41 alloy at four different temperatures of 448K, 473K, 498K, and 523K and three different stresses of 109.2MPa, 124.8MPa and 140.4MPa. The creep curves obtained in these tests show that creep resistance increased with the addition of nano-Al2O3 into the magnesium alloy, and nano-composites with 5wt% Al2O3 exhibited highest creep resistance. The values of obtained stress exponent range from 3 to 3.5, 3.55 to 6, and 4 to 6.5 for the as-cast AS41 alloy, and AS41/2wt% Al2O3, and AS41/5wt% Al2O3 composites, respectively. Thus, dislocation creep is the dominant creep mechanism. The calculated activation energies for as-cast AS41, AS41/2wt% Al2O3 and AS41/5wt% Al2O3 are approximately 66.17kJ/mol, 83.77kJ/mol, and 88.3kJ/mol, respectively. The activation energy values for the creep of composites are close to that of the pipe diffusion (92kJ/mol) of magnesium.