Abstract: In this paper，wood fiber/Al2O3 nano composites were produced by solgel technology with Al inorganic salt as the raw materials. Alsol was pushed into cell wall of poplar wood fibers though vacuumsoaking method. The performances of wood fiber/Al2O3 nano composites had been studied. In order to search the best preparing condition, the effect of moisture content and ultrasonic oscillation time on weight percent gain (WPG) had been studied: WPG of wood fiber/Al2O3 nano composites decreased with the raise of moisture; WPG of wood fiber/Al2O3 nano composites increased with increase of ultrasonic oscillation time. Infrared analysis showed O—Al—O had formed in the cell wall of the wood fibers. SEMEDX showed the sol had permeated into the cell wall and the porous structure of wood was maintained. Fiberboard was formed with fiber/Al2O3 composites and the dimensional stability and fire resistance of the fiberboard were also obviously improved.