Entropy generation due to conjugate natural convection heat transfer and fluid flow in an enclosure region was carried in the presence of a locally heat source. A thermal lattice Boltzmann BGK model is purposed to simulate the two dimensional natural convection for the governing parameters as Rayleigh number, 103≤Ra≤106 and thermal conductivity ratio of solid to fluid K=1-100. Entropy generation contours due to fluid friction and heat transfer irreversibility, isotherms, streamlines and Nusselt numbers were obtained. It is found that dimensionless entropy generation due to heat transfer (Be) decreases with increasing of thermal conductivity ratio. For Ra numbers ranging from103 to 104, the total entropy generation is mostly due to heat transfer because of relatively low velocities, but for Ra >104 the contribution due to fluid friction becomes more effective.

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