In this study, seismic performance assessment of existing low and mid-rise reinforced concrete buildings is presented by using Incremental Dynamic Analysis. Incremental dynamic analysis (IDA) is known as an accurate method and it can provide the whole range of structural responses from elastic range to collapse. The method performs a series of nonlinear dynamic analyses in which the intensity is incrementally increased for the ground motion selected to investigate the behavior until the global collapse capacity of the structure is reached. The mathematical models are prepared in the environment of Zeus-NL software, a finite element program developed especially for earthquake engineering applications. IDA curves are developed considering spectral acceleration (Sa (T1,5%)) as an intensity measure (IM) parameter. The nonlinear dynamic analyses were conducted using a set of twenty natural ground motion records selected with a range from 0.042g-3.5g peak ground acceleration and without directivity influence. In addition, the immediate occupancy (IO), collapse prevention (CP) and global instability (GI) limit states are defined based on FEMA guidelines. Moreover, the IDA curves are summarized based on 16%, 50% and 84% fractiles. Finally, conclusions are summarized based on the findings from the analysis results, while recommendations for future research are presented.