Turbulent forced convective heal transfer and flow configurations in a square channel with wavy-ribs inserted diagonally are examined numerically. The influences of file 30 degrees and 45 degrees flow attack angles for wavy-ribs, blockage ratio, R-B = b/H = 0.05-0.25 with single pitch ratio, R-P = P/H = 1 are investigated for the Reynolds number based on the hydraulic diameter of the square channel, Re = 3000-20000. The use of the wavy-ribs, which inserted diagonal in the square channel, is aimed to help to improve the thermal performance in heat exchange systems. The finite volume method and SIMPLE algorithm are applied to the present numerical simulation. The results are presented on the periodic flow and heat transfer profiles, flow configurations, heat transfer characteristics and the performance evaluations. The mathematical results reveal that the use of wavy-ribs leads to a higher heat transfer rate and friction loss over the smooth channel. The heat transfer enhancements are around 1.97-5.14 and 2.04-527 times over the smooth channel for 30 and 45 degrees attack angles, respectively. However, the corresponding friction loss values for 30 degrees and 45 degrees are around 4.26-36.55 and 5.03-97.93 times higher than the smooth square channel, respectively. The optimum thermal enhancement factor on both cases is found at R-B = 0.10 and the lowest Reynolds number, Re = 3000, to be about 1.47 and 1.52, respectively, for 30 degrees and 45 degrees wavy-ribs. (C) 2015 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.