Wake structures behind two circular cylinders with different groove configurations(U and V-shape) have been investigated experimentally. The results were compared with those for the smooth cylinder having the same diameter D. The drag force, mean velocity and turbulent intensity profiles of wake behind the cylinders were measured with varying the Reynolds number in the range of Re(sub)D=8,000∼14,000. As a result, the U-shaped groove was found to reduce the drag up to 18.6%, but the V-shaped groove reduced drag force only 2.5% compared with the smooth cylinder. As the Reynolds number increases, the vortex shedding frequency becomes a little larger than that of the smooth cylinder. The visualized flow using the smoke-wire and particle tracing methods shows the flow structure qualitatively.