Hot tear is the one of the biggest problems of cast products. There have been many researches in order to understand the formation mechanism of hot tear. However, it is still uncertain when a hot tear initiates and how it propagates. Thus, the preliminary research has been carried out to observe the vibration of permanent mold which correspond to the initiation or propagation of hot tear. Al-2.0 wt% Cu alloy was used for test alloy. The signals of acceleration sensor were recorded at an interval of 5 ms. After casting, the vibration, which lasted scores of milliseconds, was observed intermittently. This may indicate that hot tear initiates or propagates intermittently and the strain due to contraction of solidification or cooling is relaxed by hot tear.