Effect of heating rate on the microstructure of the silicon nitride ceramics has been investigated. The specimens with composition of 92Si3N4-6Y2O3-2Al2O3 (in wt%) were sintered at 176$0^{circ}C$ under 127 kPa for 3h in N2 atmosphere at various heating rates from 1 to 10$0^{circ}C$/min. The grain size of larger than 2${mu}{ extrm}{m}$ and less than 1${mu}{ extrm}{m}$ were measured and compared for the specimens. Regardless of heating rate, grain size of all the specimens showed bimodal distributions and the fracture toughness remained in the range of 5.53~5.72 MPa.m1/2. However, the aspect ratio of the grains of diameter above 2${mu}{ extrm}{m}$ increased with the heating rate while their grain size and volume fraction decreased.