Magnesium alloys are very attractive for light-weight constructions because of their relatively high strength-to-density ratios. Up to this time most of the material is used for components like cell phones, gear or clutch housings, but there is an increasing demand to use the material also for cyclically loaded structural parts and, if possible, at higher service temperatures. To model the behavior of complex components, e.g. by finite element method, materials properties must be known. Cyclic lifetimes of the wrought alloy AZ31 and the cast alloy AZ91 at room temperature as well as at temperatures up to 300 degreesC were investigated and characteristic damage parameters were determined to describe the cyclic deformation behavior. With increasing temperature plastic strain amplitudes, which are a measure for materials damage during cyclic loading, increase while cyclic lifetimes decrease. Additionally, the deformation behavior of both materials changes from cyclic hardening to cyclic softening. Already at a temperature of 150 degreesC cyclic lifetimes of both alloys were considerably reduced compared to room temperature experiments. At higher temperatures also pronounced cyclic creep was observed under stress controlled loading conditions. Cyclic creep leads to a change of the damage mechanisms influencing also the Coffin-Manson relation. For both alloys negative mean stress increases cyclic lifetimes whereas positive mean stress leads to a lifetime reduction compared to the mean stress free loading condition, for the temperature and loading range investigated.