The super-critical secondary flow properties of natural convection in an inclined channel (NCIC) have been explored numerically by virtue of Boussinesq type Navier-Stokes equations. The primary flow in the inclined channel heated from below was assumed as fully developed so that the secondary flow in the cross-section can be studied as a Benard type problem without regarding the primary speed profiles but allowing the buoyancy force depending on the channel inclination. The ratios of channel spacing to width for the inclined channel have been considered to recognize the sensitivity to the secondary flow patterns from the ratio, with the Rayleigh number changing from 10(4) to 10(6). For moderate Rayleigh numbers ranging from 10(4) to 10(5), it was revealed that the numerically evaluated spatial wavelength of the secondary flow appears a relatively good consistence with measured data, and the pattern of the secondary flow is sensitive to the inclination angle. (C) 2003 Elsevier Ltd. All rights reserved.