In order to widen the application of microcrystalline magnesite, the microcrystalline magnesite in Sichuan and Tibet area was used as the raw material to prepare light-burned MgO at 700, 800, 900, 1 000, 1 100 and 1 200 ℃ for 3 h, respectively. Then the physical and chemical properties of the light-burned MgO were detected, and its application prospect was analyzed. The results show that: (1) microcrystalline magnesite completely decomposes forming light-burned MgO calcined at the temperature range of 700-1 200 ℃; the MgO content of the light-burned MgO is higher than 96.51%; the chemical activity is 88-130 s and the grain size is 40-200 nm; it has the advantages of high purity, high activity and fine grain; (2) the light-burned MgO prepared with microcrystalline magnesite can be widely used in many industries; it can be used in refractories industry to prepare high-purity sintered magnesia and large crystal fused magnesia, or as an additive for refractory products, etc.; it can also be used in magnesium chemical industry to prepare electrical grade magnesia, silicon-steel magnesia, environmental friendly flame retardant magnesium hydroxide, magnesium sulfate fertilizer, pharmaceutical grade magnesia, food grade magnesia, etc.