In this experimental study, heat transfer from a circular cylinder placed behind an obstacle in cross-flow was investigated. In the experiments two types of cylindrical obstacles, one with circular cross-section and the other with square cross-section, were used in order to test the effect of geometrical shape of the obstacle on heat transfer from the test cylinder. In addition, the effects of obstacle size and the separation between the obstacle and the test cylinder were investigated in the interval of Reynolds numbers 1,100 less than or equal to Re less than or equal to 19,500 and for the dimensionless separation ratios ranging from 0.8 to 9. Based on the measurements, average Nusselt number was determined using lumped heat capacitance method. From the results, it is observed that the shape and size of the obstacle significantly affect the heat transfer from a cylinder in the wake flow region. (C) 2000 Elsevier Science Ltd.