Soluble conducting polypyrrole (PPy) was chemically synthesized by using dodecylbenzene sulfonic acid (DBSA) as dopant. Electrodes were prepared by solution casting on glassy carbon (GC) substrates. They were characterized by potentiometric, cyclic voltammetric (CV) and electrochemical impedance spectroscopic (EIS) measurements. PPy(DBSA) modified electrodes showed good reproducible cationic response to Ca with the sensitivity of 27.2 +/- 0.2 mV decade(-1) which remained practically constant over 10 d. The standard potential, however, was found to drift 70 mV over the same time period. The doping process of the PPy(DBSA) film was investigated by cyclic voltammetry and EIS in 0.1 M CaCl2. The most significant change in the impedance spectra of the PPy(DBSA) film takes place between -500 mV and -400 mV which coincides with the beginning of the oxidation wave in the cyclic voltammogram of the film. The impedance spectra were fitted to an equivalent circuit and the redox sensitivity of the PPy(DBSA) film was also studied.