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Quartz Crystal Microbalance (QCM) sensor coating layer as selective and sensitive material was usually made in a thin layer to avoid any damping effect on the sensor. Coating thickness in the range of nanometer was typical. The used of a thick polymer coating was known in the range of less than 3(mu)m. Usually the coating layer was prepared to support the QCM sensor to work as a mass sensitive device based on the Sauerbrey equation. A targetted biomolecule or chemical molecule was seen as a pure deposited mass on top of the sensor in the vertical direction. In our work, an ultra-thick polystyrene coating was done. The polystyrene film was formed using a spin coating method. A high concentration of polystyrene solved in toluene was used for the coating. The impedance spectrum of the QCM sensor before and after coating was measured. The fundamental resonance frequency of the sensor changed bigger than 2% and less than 5% of its initial frequency. We observed that the coating contributed little effect to the electrical impedance of the QCM sensor. The calculated film thickness was up to 8.8(mu)m, which was ten times thicker than common film coating used on a QCM sensor. The impedance of the sensor shows that the coating was still considered as glassy film.