In this study, the effect of seismic soil-structure interaction modeling simplifications on bridge analyses results is investigated. For this purpose, four structural models of bridges are built in decreasing levels of complexity starting from a structural model including the true behavior of the foundation and backfill soil and gradually simplifying the model to a level where the effect of backfill and nonlinear foundation soil is totally excluded. In the most complicated structural model, the soil is modeled as a shear-column with dashpots to simulate free-field motion and dynamic p-y curves and dashpots connected between the piles and the shear-column are used to simulate local soil-pile interaction and radiation damping. Moreover, the nonlinear dynamic interaction between the backfill and abutment is modeled using nonlinear springs and dashpots. The model is simplified gradually where three additional models are built. First, the shear-column is excluded from the structural model. Then, the dashpots used to simulate radiation damping are excluded from the structural model. Finally, the soil-pile interaction is modeled using linear springs. On all the structural models considered, two sets of analyses are conducted by including and excluding the abutment-backfill system. Nonlinear time history analyses of the modeled bridges are then conducted using ground motions with small, medium and large intensities. The analyses results are used to assess the effect of modeling complexity level on the seismic behavior of bridges. The nonlinear soil-bridge interaction is found to have considerable effects on the seismic behavior of bridges under medium and large intensity earthquakes.