The influence of experimental conditions on the electrochemical growth of poly(N-vinylcarbazole (PVCz), its morphology and electrochemical properties, in relation to its sensitivity to propylamine (PrNH2) vapour, was investigated. It was verified that water present in the acetonitrile base electrolyte used for electropolymerization plays the major role. The porosity of PVCz film decreases with increasing concentration of water up to about 20%. The work function (WF) responses of non-porous films were more reproducible and were without drifting of the signal observed in particular after initial exposure to propylamine. Fourier transform IR study demonstrated that the reason for this drift is irreversible chemisorption of propylamine. The method of electrochemical PVCz deposition by square-wave potential pulses with frequencies of tenths or hundreds of hertz was used. Modulation of the frequency has similar effects to those of water, resulting in a more or less dense PVCZ Structure. To achieve full response, the thickness of the polymeric film should be greater than that of the space charge region, which was determined to be 500 nm. Composite PVCz layers with modified adsorption properties were synthesized. giving an improvement in signal reproducibility and drifting.