Abstract: A new anti-scour device of slotted piers with a semicircular fin is presented in this paper to overcome the limitations of traditional technologies for better protection of bridge piers from local scour. This device protects riverbed by reducing the flow around the piers and its scour power. To examine the scour reduction, we have conducted laboratory tests on a scale model of a cylindrical bridge pier, using different shapes and sizes of the semicircular fin and its different installation heights combined with different locations of the pier slot. And the scour reducing effects were eveluated and analyzed by measuring the 3D geometrical characteristics of the scour pits around the piers, along with the average velocity, turbulence intensity, and turbulent kinetic energy of the flow around the piers. The results showed that scour depth was significantly reduced by the new device and its reduction in scour depth was 1.8 times greater than that by opening a slot on the pier only. And in front of the piers, the mean values of vertical average velocity, vertical turbulence intensity, and turbulent kinetic energy were all decreased obviously, with the values above the fin plate far larger than those under it. At both sides of the piers, mean longitudinal velocity and longitudinal turbulence intensity were also reduced remarkably. Thus, the device of a slotted cylindrical pier with a semicircular fin has prominent anti-scour effect and provides a basis for further studies and engineering application.