The present experimental study describes mass transfer enhancement in grooved channels with different cavity lengths for pulsatile flow. Overall and local mass transfer rates were measured by the electrochemical method with a high Schmidt number and also the vortical motion within the groove was visualized by the electrolytic precipitation method. We especially focused on the influence of oscillation frequency on mass transport enhancement. Transport enhancement by means of fluid oscillation is found to be higher in laminar flow than in turbulent flow. There is a noticeable enhancement at intermediate Strouhal numbers, depending on the cavity length and the net flow Reynolds number. It is revealed that the mechanism for a peak transport enhancement factor against Strouhal number is not explained by the hydrodynamic resonance proposed by Patera and Mikic, under a certain condition.