The problem of laminar natural convection on a vertical baffled plate subjected to a periodic oscillation is investigated numerically. Of particular interest of this paper is the heat transfer characteristic with the oscillatory velocity being close to the flow velocity in the velocity boundary layer under nonoscillation condition. The results show that a sevenfold increase in space-time averaged Nusselt number is achieved. Three mechanisms that are responsible for the heat transfer enhancement are identified. In addition, the effects of the governing parameters on the heat transfer are studied over a wide range. The heat transfer enhancement is found to be increased with dimensionless oscillation frequency and amplitude, but decreased with the Grashof number. Another interest of this paper is to optimize the geometry of baffle plates and an optimal baffle height-spacing ratio 0.25–0.50 is found for higher heat transfer rate.