Abstract: The deliquescence of high activity MgO was studied by fluidized bed reactor at normal temperature and pressure conditions.The effect of different fluidization time on the degree of MgO deliquescence was also investigated.Microscopic observation of the product was carried out by means of transmission electron microscope，the activity of the product was de- tected by citric acid method and the product was characterized by specific surface area meter.Results showed that with the extension of fluidization time，Mg（OH）₂ content increased，magnesium oxide deliquescence degree increased，the product micromorphology had also changed a lot，the surface structure become hexagonal-shaped and more compact and dense，and the product activity and specific surface area were both gradually reduced.

Key words: magnesia, deliquescence, activity, specific surface area