Si2N2O ceramics were prepared by plasma activated sintering using nanosized amorphous Si3N4 powder without sintering additives within a temperature range of 1400 degrees C-1600 degrees C in vacuum. A mixed Si-N4-n-O-n (n=0, 1...4) amorphous structure was formed in the process of sintering, and Si2N2O crystals were nucleated where the local structure was similar with Si2N2O. After sintering at 1600 degrees C, the Si2N2O ceramic was composed of elongated plate-like Si2N2O grains and amorphous phase. The Si2N2O grains showed a width of less than 100nm and a very high aspect ratio.