Abstract : Numerical simulation of natural convection heat transfer for extended rectangular fins on vertical base is performed. A Computational Fluid Dynamics (CFD) Software Fluent is used to simulate a new computational model. The simulation model is developed by taking only two extended fins and vertical base instead of simulating the entire geometry. Heat transfer rate is predicted for different fin length, height and base temperature. The results of simulations show that the rate of heat transfer depends on base temperature and geometric parameters. The numerical simulation results compared with previous experimental results show very good agreement. Therefore, the accuracy of the new computational model is verified.