This study numerically investigated two-dimensional natural convection in a square enclosure with vertical array of one circular cylinder and one elliptic cylinder at Rayleigh numbers of 10⁴≤Ra≤10⁶. A simulation was carried out based on the immersed boundary method to obtain an accurate solution. The results obtained in the present study were compared with those of two inner circular cylinders with different vertical locations from a previous study. Detailed analysis results were presented in the distribution of the flow and thermal fields and the time- and surface-averaged Nusselt numbers. The flow and thermal fields eventually reached unsteady states with time-dependent characteristics at Ra=10⁶.