Laminar natural convection flow in a square enclosure having thick conducting walls has been analysed numerically. Enclosing walls are considered to have finite conductive properties. Problem has been analysed using control volume approach and employing ghost nodes at the solid fluid interface. Outsides of the walls are kept at constant temperature. Square cavity is assumed to be filled with a Bousinessq fluid with a Prandtl number of 7.0 containing uniform volumetric sources. Rayleigh number is varied from 107 to 1012. For special cases, benchmark results compare very well with the results from open literature. Isotherms, streamlines and wall Nusselt numbers are obtained and scrutinised. Results show a significant change in the buoyant flow parameters as compared to conventional non-conjugate investigations. Especially, it has been shown that walls having high thermal diffusivity are much better suited, if the cooling of the enclosed fluid is intended. © 2001 Elsevier Science Ltd. All rights reserved.