Conducting polymers such as polvaniline and polypyrrole exhibit novel sensoric properties and are able to interact chemically or electrochemically with the species of interest for detection. In the current investigation, construction of a sensor based on an electrochemical reaction between Cr-VI and a thin layer of polyaniline, coated at the surface of quartz crystal electrode, is reported. Polyaniline was synthesized, electrochemically, at the surface of quartz crystal electrode. It was then reduced at -0.1 V versus Ag/AgCl. The modified electrode was exposed to various concentrations of Cr-VI solutions ranging from 10(-7) to 10(-1) M. Mass changes of the polymer-modified electrode due to the reaction between Cr-VI and polyaniline was found to be linear, corresponding to the concentration of Cr-VI. The experiments in both acidic and nonacidic conditions were performed. In both conditions, linear double-logarithmic calibration curves of mass change of the polymer film versus Cr-VI concentration were obtained.