The authors have developed a method to evaluate the residual seismic capacity of reinforced concrete structures damaged by earthquakes, which is employed in the Guideline for Post-Earthquake Damage Evaluation and Rehabilitation. Presented in this paper are outlines of the damage rating procedures based on the residual seismic capacity index R, defined as the ratio of residual seismic capacity to original capacity. The procedure was applied to low-rise reinforced concrete buildings damaged in recent earthquakes in Japan including the 1995 Hyogo-Ken-Nambu (Kobe) Earthquake and its validity was discussed. Good agreement between the residual seismic capacity index R and damage levels observed in damaged buildings was found. Moreover, nonlinear seismic response analyses of single-degree-of-freedom (SDF) systems were carried out. It was observed that the residual seismic capacity of a damaged RC building structure can be evaluated conservatively according to the R index employed in the Guideline, and from a practical point of view, the R index is an effective way to identify the safety of damaged structures against aftershocks.