Laminar vortex shedding behind a circular cylinder and its control using splitter plates attached to the cylinder are simulated. The vortex shedding behind a circular cylinder completely disappears when the length of the splitter plate is larger than a critical length, and this critical length is found to be proportional to the Reynolds number. The Strouhal number of the vortex shedding is rapidly decreasing with the increased plate length until the plate length (l) is nearly the same as the cylinder diameter (d). On the other hand, at 1<l/d<2, the control shows two different behaviors for the Reynolds numbers investigated. The net drag is significantly reduced by the splitter plate, and there exists an optimum length of the plate for minimum drag at a given Reynolds number. From an examination of the instantaneous flow fields, it is found that the Strouhal number modification by the splitter plate is closely related to the size of the primary vortex behind the cylinder and the length of the plate. ©1996 American Institute of Physics.