The impedance of a capacitively coupled contactless conductivity detector ((CD)-D-4) cell was experimentally examined for different cell parameters by alternative current impedance (ACImp). The effect of the gap between the electrodes and the length of the electrodes on the impedance behavior of the (CD)-D-4 cell has been studied. As a result, the impedance of (CD)-D-4 cell is largely defined by the length of the gap between the electrodes and the length of the electrodes. The impedance increases with increasing gap between the electrodes and the length of the electrodes. It could be found that tightly coupling of the electrodes to the outer wall of the capillary is needed. The axial contactless conductometric detector can be effectively described by the simplest possible equivalent circuitry consisting of a capacitor, resistor, a second resister and a Warburg impedance. These results are helpful to understand the impedance characteristics of (CD)-D-4 cell and improve its detective performance. (C) 2009 Elsevier Ltd. All rights reserved.