Nonlinear and linear 4 1 2 -layer ocean models are used to explore the dynamics of intraseasonal (20–90 day periods) zonal flow in the equatorial Indian Ocean. The model simulations suggest that the observed 40–60 day zonal surface current is forced primarily by wind associated with the Madden-Julian Oscillation (MJO), which peaks at 40– 60 days. The strongest spectral peak of zonal flow, however, occurs at 90-day period in the model and a corresponding 90-day peak appears in the observed sea level data. The 90-day current results from the preferential excitation of Kelvin and Rossby waves by the lower-frequency component of intraseasonal wind and from the enhancement by Rossby waves reflected from the eastern ocean boundary.