This paper studies the effects of the extended-column to improve seismic capacity of old buildings. The capacity curvature of buildings by the procedure of nonlinear pushover analysis of SAP2000 is gained and an intersection point of the demand spectrum and the capacity spectrum by ATC-40 suggested method is estimated for the seismic capacity of old buildings. The results will be discussed on the effects of seismic capacity by using the extended-column to retrofit the buildings and compared with that of the current seismic evaluation method in Taiwan.