Abstract: The microstructure of both {10(?)1} and {10(?)0} (directions perpendicular to the {10(?)1} and {10(?)0} planes) α-Si_3N_4 whiskers were investi- gated by high resolution electron microscopy (HREM).On one side of the {10(?)1} α-Si_3N_4 whiskers many planar defects were ob- served,two kinds of micrograins on one side of the {10(?)0} whiskers were found.In one type,sepa- rated α-Si_3N_4 (28 H) micrograins had the same orientation with respect to the matrix whisker;in the other type,connected polymicrograins consisted of both α-and β-Si_3N_4 (14H).

Key words: α-Si_3N_4 whisker, microstructure, HREM