The transient hydrodynamics and the free surface shape have been numerically predicted by CFD for an under-baffled agitated vessel during the stopping phase of the agitator, including the inertial period after the agitator has completely stopped. The simulations were carried out in a fully transient manner using a gas/liquid inhomogeneous two phase flow model coupled with a k-epsilon turbulence model. The time dependence of the system studied reveals that the history of the fluid evolution during the impeller slowing phase determines the instantaneous results, implying that the resulting hydrodynamics cannot be determined via a classical steady-state approach. The numerical prediction of the free surface shape during stopping is in agreement with experimental data.