Seismic isolation technology is one of the novel developments in the construction technology to increase the earthquake resistance of structural systems. In this study, an irregular reinforced concrete building with an L plan shape which includes all the irregularities in the plane and vertical defined in the Turkish Earthquake Code 2007 is modeled for three different base conditions. These base conditions are the fixed base and seismically isolated bases with lead rubber bearing and high damping rubber bearing. Besides these models, a regular building is also considered in this study which excludes all the irregularities except the A3 irregularity defined in the Turkish Earthquake Code 2007. Structural periods and responses obtained from time history analysis are compared with each other for the considered models. Results obtained from the study show that seismic base isolation technique applied to the reinforced concrete system improves the dynamic behavior of these systems. Although the seismic base isolation technique provides freedom in design, this outcome should not direct the architects to design irregular structures.