An unsteady numerical simulation was performed for locally forced separated and reattaching flow over a backward-facing step. The local forcing was given to the separated and reattaching flow by means of a sinusoidally oscillating jet from a separation line. A version of the k-epsilon-f(mu), model was employed, in which the near-wall behavior without reference to distance and the nonequilibrium effect in the recirculation region were incorporated. The Reynolds number based on the step height (H) was fixed at Re-H = 33 000, and the forcing frequency was varied in the range 0 less than or equal to St(H) less than or equal to 2. The predicted results were compared and validated with the experimental data of Chun and Sung (1996,1998). It was shown that the unsteady locally forced separated and reattaching flows are predicted reasonably well with the k-epsilon-f(mu) model. To characterize the large-scale vortex evolution due to the local forcing, numerical flow visualizations were carried out. (C) 2000 The Japan Society of Fluid Mechanics and Elsevier Science B.V. All rights reserved.