Abstract: In-situ formation fibrous polytype AlN composite ceramic materials was prepared from AlN-Y_2O_3-SiO_2 system.In comparison with AlN ceramics,both bending strength and fracture toughness of the composite materials are much bettered.Microstructural observation revealed that a lot of epitaxial growth fibrous AlN polytype occurred in matrix.Y_2O_3 seems to act as a densifier for in-situ formation materials and as medium for growth of fibrous polytype.SiO_2 is the growth promoter for fibrous polytype.The occurrnce of fibrous polytype may increase the strength and toughness of AlN ceramic composite mateirals.

Key words: AIN ceramics, in-situ formation, fibrous polytype