The low density of magnesium alloys makes them attractive for light weight constructions. However, important aspects are the rather poor mechanical properties of the most commonly used Mg alloy AZ91 (approximately 9 wt.-% Al, 1 wt.-% Zn), which limits its use in, e. g., power train applications. Alloying AZ91 with Ca leads to a significant improvement of creep resistance. To investigate the influence of the Ca addition on the fatigue behavior, symmetric push pull tests have been performed on AZ91 alloys with an addition of 0, 1 and 3 wt.-% of Ca, respectively. At relatively high amplitudes, the Ca containing alloys show a decrease in fatigue life compared to Ca-free AZ91. However, with a decrease in amplitude, the fatigue life of the alloy with 3 wt.-% Ca are comparable with the Ca-free AZ91 alloy and with a further decrease in amplitude the alloy with an addition of 3 wt.-% Ca has an even higher fatigue life than the Ca-free alloy. All alloys contain pores due to the casting process.