The ignition resistance was investigated for CaO added Mg-Al alloys. The ignition resistance was examined by DTA for quantitative data, furnace chip ignition test for the safety of machined chips and torch ignition test for safety of products. The ignition resistances under all conditions greatly increased by CaO addition. AES depth profile was performed to evaluate the ignition resistance in terms of surface oxide stability. In the case of Mg-Al alloy without CaO, there was the thick and porous MgO oxide layer on the surface. The depth profile for CaO added Mg-Al Mg alloys indicated that the surface consisted of the thin and dense oxide layer mixed with MgO and CaO.