In the present study, the turbulent heat transfer and fiction in a square duct roughened by continuous and truncated ribs on one wall has been investigated experimentally. The ribs are oriented transversely to the main stream in a periodic arrangement. For both cases, the rib height-to-hydraulic diameter ratio is 0.15, the rib pitch-to-height ratio is fixed at 12, and the Reynolds number varies from 8,000-20,000. Liquid crystal thermography is applied to demonstrate detailed distribution of heat transfer coefficient between a pair of ribs. The results show that the horseshoe vortices produced by truncated ribs are quite different from the flow structures altered by continuous ribs. It is noted that continuous ribs give higher heat transfer augmentation and pressure drop than truncated ribs. Moreover, the truncated ribs cannot be employed to eliminate hot spots which occur in the corresponding continuous types.