Abstract: A Quartz Crystal Microbalance (QCM) sensor coated with a thin film of PANI/MWCNT was used as a sensitive method for the determination of a number of following vapours: Acetic acid, Chloroform and Benzene. The detection was based on the absorption of the vapours of these organic compounds into the film by using gas cell chamber. The detection of these vapours can be obtained in part per million (ppm). The research includes the use of PANI/MWCNT films with different thickness (44, 62 and 92) nm where thickness of the PANI/MWCNT films was controlled by the spin coating process. Results show that increasing of sensitivity with increase of the concentration of injected analyte when the PANI/MWCNTfilm-coated QCM was exposed to the vapours of Acetic acid, Chloroform and Benzene. Best sensitivity to Chloroform and Benzene were obtained with film thicknesses 62 nm while in the case of Acetic acid best results were obtained with thickness of 92 nm.