In Japan, the seismic performance of existing RC buildings is evaluated by computing the seismic capacity index, Is, using the Standard for Seismic Evaluation of Existing RC Buildings, while the damage level of RC buildings that undergo earthquakes is assessed by the Standard for Post-Earthquake Inspection and Guidelines for Repair and Strengthening Technology. This paper reports the results of investigation of the relation between the Is value and the damage level for low-rise RC buildings designed according to the old code by conducting dynamic analysis on model buildings with a variety of Is values. The effects of the deformability type of columns and the number of stories on the relation between the Is value and the damage level were studied. Two levels of ground motions, the original level of past earthquake records and the design standard level, were considered. In the analysis, column hysteresis was derived from test results. Strength deterioration after shear failure and axial collapse that are commonly associated with hysteretic behavior of old columns, were considered. The method presented in this study enables assessment of the damage level of buildings and the damage condition of columns if the deformability type of columns, number of stories, Is value and ground motion are given. In addition, the assessed damage level of buildings are compared with the observed damage level from past earthquakes and the Is value required to prevent collapse of buildings is discussed.