Non-linear analysis is the best method to make sure that the existing or new building is safe against earthquake. Meanwhile structural irregularity is one of the major causes of damage under seismic shaking. Mainly there are two types of structural irregularity i.e. plan irregularity and vertical irregularity. Plan irregularity can cause torsional effect, while vertical irregularity increases the seismic demand in certain stories. So it has to be studied properly for the existence of the building with acceptable damage under seismic effect. This paper evaluates the seismic performance of G+9 multi-storey reinforced concrete regular building and building with plan irregularity. The buildings are assumed to be located in the seismic zone III and the analysis has been done by nonlinear static (pushover) and nonlinear dynamic (time history) analysis using the software ETABS2016. The main parameters that are considered are performance point, lateral displacement, storey drift, base shear, column shear and moments. © IAEME Publication.