Abstract: A flat heat exchange tube comprises an upper wall, a lower wall, right and left side walls interconnecting right and left side edges of the upper and lower walls, and a plurality of reinforcing walls connected between the upper and lower walls, extending longitudinally of the tube and spaced apart from one another. The tube has parallel fluid passages formed inside thereof and extending forward or rearward. Each of the reinforcing walls has a plurality of communication holes arranged at a spacing longitudinally thereof for holding the parallel fluid passages in communication with one another therethrough. The upper surface of the lower wall is provided at a portion thereof forming each of the fluid passages with a plurality of turbulence producing portions extending over the entire width of the fluid passage and arranged at a spacing longitudinally of the passage.