This work studied the thermal convection under various slip boundary conditions in a 2D box with aspect ratio equal to two. The slip parameter is the normalized tangential momentum accommodation coefficient (TMAC, 0 <= sigma <= 1). The results show that the slip boundary conditions of vertical side walls (a,) and horizontal plates (o-h) will affect the pattern selections of the flow and temperature fields. When sigma(h) < 0.02, the pattern is the one-roll mode for all sigma(v). When sigma(h) <= 0.02 and sigma(v) <= 0.1, the fluids prefer the two-roll mode where two rolls make the fluids to move upwards in the middle of the box. While sigma(h) >= 0.02 and sigma(v) >= 0.2, the fluids prefer the other two-roll mode which makes the fluid to move downwards in the middle of the box. (C) 2010 Elsevier Ltd. All rights reserved.