Al2O3 ceramic fillers were incorporated into polyetheretherketone (PEEK) to improve the mechanical property in order to suit its aerospace application. To get the high performance composite, it is important to control the dispersion of the nano-Al2O3 among the PEEK matrix. As a pre-fabrication process, the dispersion behaviors of the nano-Al2O3 particles in the liquid medium were studied. Thestability of suspensions was characterized by zeta potential, sediment volume, viscosity and TEM analysis. The mechanism of dispersing nano-Al2O3 aqueous suspension has been investigated including single-electronic stabilization, steric stabilization, and electrostatic stabilization. The highly dispersed and stabilized nano-Al2O3 aqueous suspensions were obtained at acidic condition (pH=3) with PEG-400 and tri-ammonium citrate (TAC).