Mechanical properties and high temperature deformation behavior of AZ31-0.84%Sb alloy have been studied. The results show that small additions of antimony to AZ31 alloy effectively enhanced the creep resistance and the ultimate tensile stress of the alloy at elevated temperature. One of the reasons for the improved high temperature properties is the high volume fraction (~20%) of the precipitates, as Mg3Sb2, which effectively hindered the movement of dislocations during the elevated temperature deformation. Considerable amounts of twins were formed during creep failure of AZ31-0.84%Sb alloy. Within the twins, many dislocation pile-ups were present on both basal and non-basal plane of magnesium matrix.