This paper presents the results of an experimental study conducted on pressure drop for flow in a square channel with two cylinders in tandem arrangement. In the study special attention is paid to the effects of the shape and size of the upstream cylinder and the separation between the upstream and downstream cylinders. In the experiments two types of upstream cylinders, one having a circular cross-section and the other having a square cross-section in three different sizes; D=d, D=2d, and D=3d, respectively were used. The size of the downstream circular cylinder was kept constant at d and the distance between the tandem cylinders was varied in the interval 1.0 <= S/d <= 10.0. The effect of Reynolds number on pressure drop was also studied in the range of 52,100 <= Re <= 156,000. Results show that the distance between the cylinders significantly affects the pressure drop in the channel. At certain range of distance between the cylinders, the pressure drop takes smaller values comparing to pressure drop in a channel with single upstream cylinder. (c) 2007 Elsevier Ltd. All rights reserved.