Abstarct: In this study, dynamic responses of isolated and fixed baxse RC building with and without soil structure interaction (SSI) under near fault and far field earthquakes are investigated. For this purpose, three RC building of 4, 8 and 12 story with and without lead rubber bearing (LRB) isolators were modeled in Opensees software and generally six records of near fault and six record of far field ground motions which had the same components but different stations, conducted to each of this models. The analysis that used in this study is incremental dynamic analysis (IDA) in which, by applying a vast range of scale-up records of earthquakes to structures, receiving relevant responses, categorizing and presenting them, the behavior of such structures is understood as better and deeper. The results of the study were interstory drift ratio, baxse shear, roof displacement and acceleration. The results showed that the isolators in the isolated structures greatly reduce the structural responses by absorbing the earthquake energy and will help to economize of the projects. Considering the effects of soil structure interaction in isolated buildings is important and in actual PGA, near fault records generate bigger results than far field records but in same PGA, far field records generate bigger results.