In recent years, research and development work have been done on surgical robots and navigation systems. Although these systems have potential to realize minimally invasive and precise surgery, it is considerably difficult to control these robots accurately because organ sometimes shows unanticipated behavior during operation. Therefore, the robot control system which can respond to the various change of surgical situation is required. The purpose of this study is to develop organ biomechanical simulators which predict organ behaviors and give some information about organ state to robot control unit. In this research, we developed two types of biomechanical simulator for RF ablation therapy. One is organ deformation simulator using physical property of liver to predict position change of tumor during needle insertion. The other is organ temperature distribution simulator using thermophysical property of liver to predict temperature change of tumor during tumor ablation. As a result of validation experiments of simulation accuracy, it was proved that these simulators had enough effectiveness to predict the organ behavior during RF ablation therapy.