In this paper, the effect of rib spacing on heat transfer in a rotating two-passage channel (aspect ratio, AR=2:1) at orientation angle of 135 deg was studied. Parallel ribs were applied on leading and trailing walls of the rotating channel at the flow angle of 45 deg. The rib-height-to-hydraulic diameter ratio (e/Dh) was 0.098. The rib-pitch-to-rib-height (P/e) ratios studied were 5, 7.5, and 10. For each rib spacing, tests were taken at five Reynolds numbers from 10,000 to 40,000, and for each Reynolds number, experiments were conducted at four rotational speeds up to 400 rpm. Results show that the heat transfer enhancement increases with decreasing P/e from 10 to 5 under nonrotation conditions. However, the effect of rotation on the heat transfer enhancement remains about the same for varying P/e from 10 to 5. Correlations of Nusselt number ratio (Nu/Nus) to rotation number (Ro) or local buoyancy parameter (Box) are existent on all surfaces (leading, trailing, inner and outer walls, and tip cap region) in the two-passage 2:1 aspect ratio channel.