The obtained results of direct numerical simulation of the free mercury convection in a rotating cylindrical container heated from below are presented. Setting the Prandtl number equal to 0.025 and the height-to-diameter ratio equal to 1.0, effects of container rotation and heat transfer in horizontal solid walls have been studied. The effective Rayleigh number was close to 106. The Navier – Stokes equations, written with the Boussinesq approximation, were solved using the fractional-step method. The instant and time-averaged flow fields, the pulsation spectra and the integral heat transfer data were analyzed. The in-house code SINF/Flag-S results were compared with the available experimental data, and with the data obtained using the commercial software ANSYS Fluent 15.0.