Two proposals for modeling of the base isolators as a structural element have been given. The first model simulates base isolator as two springs, while the second one models base isolator as a deep beam element. Comparison between the two models indicates that if the experimental data to determine the value of EI/L are available, the modeling of base isolator as a deep frame element will be more accurate than the model of two springs. In both models, the energy dissipation in the base isolators has been modeled by an equivalent viscous damping. Based on the comparison with experimental work it is has been found that the equivalent viscous damping can simulate the response of lead - plug rubber bearing with a lower accuracy if compared with modeling the response of low damping rubber bearing. This is mainly due to approximate simulation of inherent nonlinearity nature of lead - plug rubber bearing.