. A method for evaluating the seismic capacity of existing reinforced concrete (R/C) building was developed by implementing a diagonal strut model for considering brick infill effects. In this model, the strut width is presented as a function of frame-infill contact length, which was evaluated by static equilibriums related to compression balance and lateral displacement compatibility at the frame-infill interfaces. The lateral strength and stiffness of infill were obtained based on the strut width. The strut model has been verified through comparison with experimental results of a brick masonry infilled R/C frame. Good agreements were observed between the experimental and analytical performance on the lateral strength and ductility of the infill. Consequently, the diagonal strut model can be an effective tool for precisely screening earthquake-vulnerable existing R/C buildings in Padang city. In this study, two calculations of seismic capacity of two stories existing R/C building, without and with considering brick infill effects, were conducted by applying the diagonal strut model. However, the seismic capacity of R/C building without infill effect was evaluated based on Japanese standard. Consequently, it reveals that the brick infill significantly affected the seismic resistances of the investigated building.