This study investigates the effects of boundary wettability on the turbulent natural convection heat transfer in a rectangular enclosure. Two water contact angles (theta) of the bottom copper plate of enclosure, 100 and 162 degrees, were established using a sol-gel method. The contact angle of the copper plate without surface modification (the plain surface) was approximately 95 degrees. This study presents the measured results of the Rayleigh number (Ra) and the Nusselt number (Nu) for these three surfaces at three aspect ratios (AR = W/H) of 0.5, 1, and 2 for Rayleigh numbers ranging from 7.49 x 10(4) to 1.36 x 10(7). A power-law correlation is proposed to fit experimental results on the plain surface. As for the modified surfaces within the range of Rayleigh number studied, the results show that Nusselt numbers on the superhydrophobic surface are approximately 16% lower than predicted values obtained from the correlation on the plain surface. However, there is little difference in the Nusselt number between the plain surface and the superhydrophilic surface. (C) 2013 Elsevier Ltd. All rights reserved.