On 8 grades of porous ceramics which have various pore sizes and their distributions, bending tests were carried out to clarify correlation between strength and microstructure. To identify fracture origin, in-situ observation technique using high speed camera was developed. In most cases, the linking pore was observed at fracture origin on surface or nearby surface of specimen. Correlation between microstructure of porous ceramics, linking pore size and strength was formulated on the basis of point stress model. Strength was well correlated with a parameter which is the linking pore size non-dimensionalized by average diameter of skeleton structure. According to the relational expression, it was predicted that the larger pore size leads to higher strength in the case of comparable porosity.
