Coupled heat transfer between two laminar natural convection systems separated by a vertical conductive wall is theoretically analyzed, taking account of the two-dimensional thermal conduction in the separating wall. Numerical solutions of temperature fields for both fluid flows are combined with the analytical solution for the wall so as to satisfy the continuity of the temperature and the heat flux at both sides of the conducting wall. Obtained results of the whole temperature field show that the axial conduction effect in the wall is substantial when the wall is thick and has a high thermal conductance, and that axial conduction in the wall is found to relax the interference between the two convections in both fluids. Experiments have been conducted for air-air systems with the conducting wall made of aluminum or glass. Theoretical predictions describe well the experimental temperature distributions, showing the validity of the present analysis.