AbstractIn this study, the effects of infill walls to the response of a selected building under earthquake loading were investigated. Although various suggestions have been offered, designers usually neglect the effect of infill walls on building behaviour when designing a building. In this study, the effects of infill walls on a building, which consists of two storeys of basement, one storey of ground floor, one storey of mezzanine floor and 10 storeys of flats, were investigated. Three‐dimensional models of the building with and without infill walls were modelled in SAP2000. Then, nonlinear time history analysis was performed on the models with and without infill walls. Infill walls were modelled both as mass and structural elements. The results of two analyses were compared. Consequently, the effect of infill walls on the behaviour of buildings such as period, maximum roof displacement, base columns end‐forces and soft‐storey formation coefficient was determined. Addition of infill wall to the structures caused changes in maximum roof displacement, modal periods, maximum base column end‐forces, shear force and soft‐storey formation coefficient. Copyright © 2008 John Wiley & Sons, Ltd.