This paper presents a description of a computer simulator, namely, FBRSim, which simulates the thermal-hydraulics of fast breeder reactors (FBRs). It was design to be used for learning and research purposes. It simulates the temperature field, the heat transfer rates, and the pressure drop in typical FBR fuel assemblies. Furthermore, it simulates the core inlet and exit temperature and pressure. The simulator consists of six main modules, these are: geometrical, radial and axial temperature distribution, pressure drop, heat transfer rates, volumetric source strength, and physical properties modules. The modules carefully selected to help with analyzing and exhibiting all of the important thermal-hydraulic trends of typical FBR. In order to demonstrate the flexibility and advantages of using FBRSim for learning and research purposes, it was used to simulate typical FBR condition using the simulator default data. The simulation results demonstrate that FBRSim can be considered as a powerful learning and research tool, which can be easily used by undergraduate and postgraduate students to simulate and investigate the performance of FBRs under different geometrical configurations and physical and operation conditions.