As ceramics have corrosion resistance, they are generally used in the corrosive environment. In general, fatigue strength is reduced with the elapse of time in the corrosive environment. Such a phenomenon occurs not only in acid/alkalis environment but also in water one. Even in the air, however, the influence by the constitution of moisture content is also considered. And, even in water environment it is thought that the resistance of crack propagation of ceramics increases by the increase of crystal grain and cracks form and that the progress of corrosion is also prevented by the protection action. Therefore, we must solve those problems. At present the corrosion of ceramics in water environment has been hardly examined. From the standpoint mentioned above, we tried the fatigue tests by using the glass ceramics in various kinds of environmental conditions such as air, ion-exchange water and seawater. That is to say, for glass ceramic specimens with the three collinear cracks which introduced the different crack center distances by Vicker's indentation, the cyclic fatigue tests in water environment were carried out with four-point bending load. It was found that the time to failure for glass ceramic specimen (N-0) in which the crystal grain is small in water environment decreased significantly in comparison with the atmospheric condition, while in the ceramic one (N-11) in which the crystal grain is large, the difference of that due to the environment can not be observed and that in the case of the glass ceramic N-0 specimen, the repetitive fatigue life under the condition of sea water environment has lower tendency than those of the conditions of atmospheric/water one at the range of the low stress.