Experimental and analytical studies on fracture toughness of alumina ceramics used as IC plate were carried out. Material used was 96% alumina ceramics. Four point bending test method was adopted to estimate fracture toughness. Notches were introduced for various length ranging from 0.02mm to 0.2mm. Following results and conclusions were obtained. The fracture toughness obtained by conventional fracture mechanics approach is apparent one and increases with an increase of precrack length and shows a constant value in the range of larger crack length. This characteristics was explained by the interaction between a main precrack and inherent microcracks or voids near in the crack tip. When main crack length becomes shorter, the interaction between main crack and voids or microcracks are not negligible. So continuum mechanics can not be applied and it should be treated as porous materials. But when crack length becomes longer to some specified value, these effect becomes less evident. For such case, macroscopic fracture mechanics can be applied to the estimation of fracture strength. Physical considerations based on micro mechanics was carried out to understand these phenomenon mentioned above. These results will be useful when a notch is introduced in an alumina green sheet in order to break down an IC substrate after sintered with the dimension designed.