Many industrial, medical, environmental, and military applications require sensitive, selective, fast, and stable gas sensors to detect and measure the concentration of gases in the environment. A group of mature and important gas sensors are the Quartz crystal microbalance (QCM) sensors. Low price and good selectivity are the desirable features of this type of sensors. In the present study, QCM sensors were fabricated and characterized to detect volatile organic compounds and, in particular, to detect Dimethylacetamide and alcohol vapors. In the first part of this research, the APTES adsorption layer was fabricated by using the sol-gel process and drop coating on the electrode surface. The microstructural and chemical properties of the layer were tested using FE-SEM, EDS and FT-IR methods. Gas sensing experiments were performed with the polymer coated sensors exposed to the vapor of various volatile organic compounds. The highest sensitivity with excellent selectivity was obtained for a sensor with a layer thickness of 2.5 ?m which was equal to 0.66 Hz.ppm -1 toward Dimethylacetamide which is a polar solvent. By examining the sensors, an experimental relationship was obtained for the sensitivity of the sensors as a function of the device frequency and sensing layer thickness. The mechanism of vapor sensitivity was investigated using the linear solvation energy relationship (LSER) model. The study of the response of a sensor in a long time showed that in the fabricated sensors, humidity has the greatest effect on the sensor baseline and on the other hand, ambient temperature is the most important factor in determining the sensitivity of the sensor. In the second part of this research, sensors with higher operating frequency and smaller dimensions equipped with zinc oxide coating were fabricated using ultrasonic assisted deposition from solution. The structure of the sensing layer and its constituent atoms were investigated by FE-SEM and EDS analysis. According to experiments, the sensors were sensitive to primary alcohols. The highest vapor sensitivity recorded among the fabricated sensors was 0.26 Hz.ppm -1 for 1-propanol vapor. According to the experiments, increasing the length of the carbon chain amplifies the dispersion forces in alcohol vapor and this increases the number of molecules adsorbed in the sensing layer which improves the gas sensitivity of the sensor. واژگان کلیدی انگلیسی: Gas sensor, Quartz crystal microbalance, Volatile organic compounds, Oscillator circuit.