In order to develop the non-combustible Mg alloys with high oxidation resistance, the effects of Ca and Be additions on high temperature oxidation and combustion behavior of AZ91 alloys have been studied. The ignition temperatures of the AZ91 alloys containing 0.3-5 wt% Ca and 0.002-0.006 wt% Be were noticeably increased by forming the compact and dense oxide layers consisted of MgO, CaO and BeO. The oxide layers on the surface were analyzed using optical microscope, FE-SEM equipped with EDS, low angle XRD and AES in order to investigate the ignition proof mechanism in the molten alloys. Microbalance was also used to measure the weight changes due to oxidation of Ca- and Be-bearing AZ91 alloys, which showed the excellent oxidation resistance at elevated temperature.