A two-dimensional single-phase natural convective heat transfer in a cavity with centrally located thin partition utilizing nanofluids has been numerically analyzed. The nanofluid used, which is composed of aluminum nanoparticles in suspension of Benzene, was provided at various solid volume fractions. The study is carried out numerically for a range of Rayleigh numbers, solid volume fractions, partition heights, and aspect ratios. Regions with the same velocity and temperature distributions are identified as a symmetry of sections. One-half of such a rectangular region is chosen as the computational domain, taking into account the symmetry about the thin partition. The governing equations are modeled by a stream function-vorticity formulation and are solved numerically by finite-difference schemes. Comparison with previously published numerical and experimental results showed excellent agreement. It is demonstrated that the partition height has a strong effect on both the heat transfer rate and the flow pattern. Results are presented in the form of streamlines and isotherm plots. The variation in the local Nusselt number along the thin partition provides valuable insight into the physical processes. A new correlation is proposed for the heat transfer studies in a wide range of thermal and geometric parameters.