The two-dimensional velocity and direction of liquid flow were measured in the downcomer of concentric airlift reactors by a cross-correlation method utilizing a three-electrode electrochemical probe. The process of eliminating the part of bubble signals was necessary and developed systematically. The optimum value of the distance between the microelectrodes was decided for the gas-liquid two-phase now. The circulation velocities obtained with this probe agreed with those by a solid tracer method. When the ratio of the diameter of the draft tube to that of the column was small (D-i/D-o=0.29), circumferential components of the liquid velocity as well as vertical components were detected to be significant at higher superficial gas velocities.