_{:Magnesium oxide aerogels were made by sol-gel process using magnesium methoxide as precursor,methanol and deionized water as solvents followed by ethanol supercritical fluid drying. The influences of the different factors on the gel time and the specific surface area of magnesium oxide aerogels were studied, and the structure and morphology were characterized by Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), Transmission Electron Microscope (TEM) and X-ray diffraction (XRD), and the Small Angle X-ray Scatter (SAXS) was utilized to determine the fractural structure of the magnesium oxide aerogels. The results show that MgO aerogels are typical mesoporous materials with the average pore size of 19.6 nmand possessrich network,high porosity(98%), high specific surface area(904.9 m2/g) and low density(0.055 g/cm3). The resultsof SAXS analysis show that the fractal dimension of the MgO aerogels is 2.32 in high q area which proves the existence of rough surface and pore fractal structure.}