Abstract: Three kinds of high-purity Al₂O₃ powders, whose average particle size is 0.1, 0.3 and 3.0 mμ respectively, were used as the starting power, and their compacts were fired in the radio-frequency plasma generated at a pressure of 80 Pa using N, as the working gas.Experimental results show that the 0. 1 and 0.3 mp powder compacts can be sintered to nearly the theoretical density within 60 s and this sintering is almost finished in the heating period. It is concluded that the mechanism of liquid sintering, the electric charge effect of Al₂O₃ powder, and the effect of tempetrature gradient in the compacts can affect simultaneously on the rapid densification of the compacts in the plasma sintering.