A numerical analysis was carried out to study the laminar natural convection in an enclosure induced by a heated backward step. The effects of the Rayleigh number Ra, the Prandtl number Pr, and geometrical size of the enclosure on the flow structure and heat transfer characteristics are investigated in detail. Results reveal that the presence of the backward step can enhance the heat transfer coefficient about 32% for Ra = 10(7) and Pr = 0.71. The extent of heat transfer enhancement increases with the decrease in Ra. The influence of the dimensionless distance between the heated backward step and cooled plate L-2 on the average Nusselt number (Nu) over bar is more significant for the system with a smaller Ra. A larger dimensionless height of the insulated vertical plate H-2 results in a higher (Nu) over bar. For H-2 = L-1 = L-2 = 1, Pr = 0.71, and 10(3) less than or equal to Ra less than or equal to 10(7), the average Nusselt number can be correlated as (Nu) over bar = 0.353Ra(0.256).