Earthquake forces have always been considered as a threat to the structures. One of the most effective ways to have structures with minimal damage and improve their resilience is prevent transmission of earthquake forces to the superstructures. For this purpose, the base isolation method can be implemented. Common types of base isolators are elastomeric rubber bearing and lead rubber bearing. Elastomeric rubber bearing is consisting rubber layers and intermediate steel plates that are produced by vulcanization process and lead rubber bearing (LRB) is similar to the elastomeric rubber bearing but a lead core is located in the center. In this study, shear behavior and vertical stiffness of LRBs are evaluated with the finite element approach. Validation analysis was performed which indicated the accuracy of modeling and then two full scale circle LRBs were selected from Bridgestone corporation with 1000 and 600mm diameters. The main purpose of this paper is evaluating the effect of lead core size, number and location on the shear behavior and vertical stiffness of lead rubber bearings.