Procedures of quantitative estimation of the earthquake damage to the gravity quaywall was studied for the earthquake preparedness. The earthquake damage episodes of gravity quaywalls were collected for past earthquakes and the quantity to give the level of the earthquake damage and the classification of the failure mode
were analysed. The estimation method to give the quantity of the damage (displacement and cost) was presented, using the ratio of the corresponding seismic coefficient of the ground acceleration to the seismic coeffcient which gives the safety factor of one in the stability analysis of the design standard. Then an optimum seismic coefficient from an economical viewpoint was studied for the rational seismic design, based on teh quantitative estimation method of the cost of damage.