Since mountain tunnels are generally surrounded by stable ground, their displacement during seismic activity tends to be minimized, making such structures less susceptible to seismic damage. Despite this, many railway mountain tunnels have sustained damage, from the 1923 Kanto Earthquake to the 2004 Niigataken-Chuetsu Earthquake. This paper provides an outline of the historical damage to mountain tunnels in Japan and outlines the results of case studies on damage sustained in mountain tunnels. Also outlined here is a classification of the damage patterns and the conditions of damage based on the results of the case studies, and we refer to the estimated causes of damage to tunnels in the 2004 Niigataken-Chuetsu-Earthquake.