After an earthquake, it is important to evaluate the residual seismic capacity of damaged buildings in order to determine the necessity of repair and retrofit and to make an efficient recovery plan. In this regard, a Japanese guideline developed by the Japan Building Disaster Prevention Association (JBPDA) “Standard for Post-earthquake Damage Level Classification of Buildings 1) ” is currently in use in Japan to estimate the residual seismic capacity of structures based on an index named R. The R-index represents the ratio of seismic capacity before and after the earthquake. The R-index calculation is intended to be a simple seismic evaluation method that does not require complicated analysis. However, this simplified method is based on the assumption that the ultimate deformation capacity of all members is the same; thus, it is not practical for assessing dual systems, such as reinforced concrete (RC) buildings containing both moment resisting frames and walls. The main objective of this study is to propose a new evaluation method to determine the R-index for buildings of mixed structure types. The proposed method uses two factors: (i) explicit consideration of different deformation capacities of structural members, θu, and (ii) a seismic capacity reduction factor, ηW 7) which considers the hysteretic energy absorption reduction of each structural member based on the observed level of damage. The available JBDPA method and the proposed method are assessed using results obtained from a shake-table test of an RC building.