The heat transfer and pressure loss characteristics on a square channel with two opposite surfaces roughened by high blockage ratio ribs are measured by systematic experiments. Reynolds numbers studied in the channel range from 1 400 to 8 000. The ratios of rib height to hydraulic diameter (e/D) are 0.2 and 0.33, respectively. The ratio of rib spacing to height(P/e) ranges from 5 to 15. The rib orientations in the opposite surfaces are symmetrical and staggered arrangements. The results show that the heat transfer coefficients are increased with the increase of rib height and Reynolds number, though at the cost of higher pressure losses. When the rib spacing to height ratio is 10, it keeps the highest heat transfer coefficient in three kinds of rib spacing to height ratios 5, 10 and 15. The heat transfer coefficient of symmetrical arrangement ribs is higher than that of the staggered arrangement ribs, but the pressure loss of the symmetrical arrangement ribs is larger than that of the staggered arrangement ribs.