Al1-xMgx (x=0.1, 0.2, 0.3, 0.4, 0.5) alloys (designated here after as AlMg alloys) were prepared by mechanical ball milling. The thermites were prepared by sonication dispersion method. AlMg/KMnO4 thermites with different Al/Mg ratios were investigated by differential scanning calorimetry (DSC), ignition and combustion measurements. The results show that the reaction temperatures of AlMg/KMnO4 thermites decrease obviously with the increase of Mg contents, indicating that the thermal reactivity of AlMg/KMnO4 thermites is superior to that of Al/KMnO4. Furthermore, it is found that both the reaction temperatures and the burning velocities of AlMg/KMnO4 thermites decrease from 723 to 493 K, and from 254 to 204 mg/s, respectively, as the content of Mg increases from 0.1 to 0.5, among which the Al0.5Mg0.5/KMnO4 thermite displays the largest flame splash range. It is expected that AlMg/KMnO4 will be the most promising energetic material in ordnance applications