The tsunami damage due to the 2011 Tohoku earthquake were summarized, and the preparedness for the Nankai Trough earthquake tsunami was discussed. In the disaster, underestimation of the assumed tsunami and tsunami warning, delay in damage evaluation, and tsunami-related phenomena (sediment transport, topographical change, drifting objects, disaster debris, evacuation behavior, etc.) caused to increase the damage. After the disaster, assumption of the maximum class tsunami has been introduced, and numerical analysis and observation system of tsunamis have been developed. They make progress to prevent underestimation of tsunami warning and to grasp the damage promptly. However, there are still some problems to be solved in tsunami warning, such as tsunami earthquake, heterogeneity of tsunami source, and its cancellation. In addition, there are some technologies that have not yet been utilized in the real field of disaster. It is necessary to continue efforts to improve disaster management capabilities.