The response of the building to an earthquake not only depends on the characteristics of the building but also on those of earthquake ground motion. The present study intends to analyse the effect of frequency content parameter on the various response of the irregular building with and without base isolation. The study considered a medium-rise C-shaped building and modelled it in SAP2000. A non-isolated building was modelled at first to generate the required date to develop a base isolated building by incorporating a high damping rubber bearing. Two ground motion with different characteristic were chosen and time history analysis was carried out for the building models. It was found that the base shear, storey displacement, and inter-storey drift was proportional to frequency content but only for non-isolated building, while the torsional irregularity ration was proportional to frequency content for base isolated building.