In order to estimate exactly the reliability of the service life of a pressure-proof connector made of polycrystalline alumina, static and cyclic fatigue of polycrystalline alumina and its brazing part were examined. Static and cyclic fatigue tests and also static bending tests under 4-point bending loads were carried out using three types of specimens : A ; plates, B : plates with a center hole and C : plates with a center hole brazed to Cu pin with Ag-Cu alloy. Fatigue failures of both A and B specimens were basically controlled by the static fatigue stress corrosion cracking, but in addition the effect of cyclic stress on their failures could be recognized from estimating the time to failure under cyclic stress based on the data in in static fatigue tests. On the other hand, fatigue failures of C specimens were mainly controlled by cyclic fatigue like metal fatigue. This is because the main mechanism of fatigue in C specimens is the initiation of fatigue crack in the brazing alloy.