Seismic isolation is an important and widely used method to protect a structure from the devastating effects of earthquake ground motions. Seismic isolation seeks to mitigate the effects of the ground motions by decreasing the base shear acting on the structure by increasing the fundamental time period of the structure in question. This in turn affects the spectral acceleration and hence the base shear. This thesis deals with investigating the behavior of lead core rubber isolators, on bridges, under near field and far field earthquake loading. The earthquake records were scaled to three intensities, namely, very high, high, and medium to high. The parameters investigated were the longitudinal base shear, transverse base shear, longitudinal displacement and transverse displacement caused by a wide range of scaled earthquake load intensities. SAP 2000 was used to run the analysis on different bridge models which varied in the number of spans, length of span and the height of the columns. The lead core rubber isolators used in the models varied in the longitudinal and transverse stiffness. The isolator stiffness ranged from 90 kips per feet to 270 kips per feet. The results showed that the isolators reduced the longitudinal base shear for most cases. With the use of isolators there was also an increase in displacements. The results in the transverse direction showed variability which was caused by not smoothing out the response curves for the ground motions in the transverse direction. The results also show that care has to be taken when using isolation for bridges in locations with very high intensity earthquakes. For medium to high intensity earthquakes, isolators with initial stiffness between 90 to 270 k/ft can be used. For bridges in extreme earthquake zones, the use of isolators should be evaluated based on the earthquake record used and the bridge properties. The results also show that using isolators for bridges with less flexible substructure resulted in a greater reduction in base shear for most cases. The use of isolators with high initial stiffness, resulted in lower base shears in far field cases when compared to near field cases.