In the paper, the possibility of an application of an electrochemical method for the studies of the mass transfer process within the boundary layer at vicinity of the wall of the agitated vessel has been analysed. It has been proved that experimental results obtained by means of the small measuring sensors should be corrected. An effect of a size of an electrochemical sensor used for the measurements of the local mass transfer coefficient has been determined theoretically and experimentally. The values of the correction factor p evaluated from numerical simulations and experiments are in an agreement.