The present study focuses on the turbulent natural convection heat transfer in an enclosed rectangular container having high aspect ratio. The container is composed of the heated and cooled plates. The working fluid is air when the value of Rayleigh number is small, and is water when the value of Rayleigh number is large. The numerical simulation is investigated at the same time in order to elucidate the experimental results. It is obvious that the numerical computation and the empirical investigation are well correlated with the heat transfer correlation proposed previously.