Seismic retrofit of existing vulnerable buildings is important to reduce damages during earthquakes. In this paper, seismic performance index, Is, of school buildings, which were seismically evaluated and/or retrofitted by Sendai city, were analyzed and Is-index distribution for all the reinforced concrete school buildings was estimated. Improvement of seismic performance as a result of retrofit and mitigation of predicted damage ratio were presented. Moreover, retrofitting cost and expected loss were compared and validity of seismic retrofit was discussed from the point of cost effectiveness.
