An experiment was performed to investigate the transfer of thermal energy by natural convection from molten sodium to a cold plate. A large tank of sodium was used to simulate a semi-infinite mass of sodium. A horizontal circular plate in intimate contact with the sodium surface was cooled by flowing tetralin which caused its temperature to be lower than the sodium bulk temperature. As a result, natural convection occurred in the sodium and thermal energy was transferred from the sodium to the plate. Data were collected at steady-state conditions for values of the Rayleigh number ranging from 4.8 × 106 to 4 × 107. It was found that the experimental results could be correlated by the expression where Nu is the Nusselt number, and Ra is the Rayleigh number. The calculated probable error in the Nusselt number given by the above equation is 1.08, and the multiple correlation coefficient for the experimental results and the equation is 0.954. The above result is shown to be consistent with the results of other investigators who used different fluids in physical systems somewhat similar to that used in this experiment with sodium.