Fatigue behavior of SiC fiber reinforced SiC matrix (SiC/SiC) composites was carried out under bending conditions to investigate the fatigue damage and failure mechanisms. It was found that fatigue cracks initiated at several sites and then grew or coalesced each other. Finally, a crack grew significantly as a main crack to cause the specimen failure. The change of rigidity during fatigue tests was measured. The rigidity decreased with increasing fatigue damage in the specimen. Although the relationship between rigidity and number of cycles depended on applied stress, fatigue failure occurred when the rigidity reduced to a critical value. The change of the rigidity was considered to be a useful parameter to evaluate the fatigue damage of SiC/SiC composite material.