In the structural design of ceramics components especially for graphite materials, it is important to apply the realistic fracture model in the design method so as to reduce the large safety margin. In this study, we proposed the multiaxial strength model by expanding the microstructure based brittle fracture model applicable to both uniaxial tensile and compressive stress conditions. The advantage of the model is a treatment of the microstructural information such as grain size, pore size and pore size distribution. The proposed model was applied to biaxial strength prediction of near isotropic nuclear graphite using grain/pore related microstructure parameters. Predicted results were compared with biaxial strength data, and it was found that the proposed fracture model showed fairly good strength prediction.