Hydrogen gas is a source of renewable energy and has many applications such as chemical production, fuel technology, fuel for cars, rocket engines and so on. Hydrogen gas is colorless, odorless, tasteless, flammable and explosive at concentrations of more than 4% in any environment and cannot be recognized by the human senses. With the increasing usage of hydrogen as well as the increased risks in the field of storage, safety and detection of hydrogen gas, research has received much attention in the field of manufacturing the inexpensive sensors in a wide range of concentrations. Therefore, in this study, the fabrication of a flexible hydrogen gas sensor using sputtering of molybdenum oxide layer on a polyester fabric has been studied to detect hydrogen gas at room temperature. The idea of using the molybdenum oxide layer as a gas sensor is iired by its coloration due to the adsorption of hydrogen gas. The manufacturing process is simple and inexpensive, and the sensor can be mass-produced. It should be noted that the use of polyester fabric and molybdenum oxide coating in the construction of gas sensors has been studied for the first time. In order to analyze and characterize the fabricated samples, X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) analysis were performed. Also, the data related to the color change of the gas sensor has been measured in a simple way using an electronic color sensor. The effect of partial oxygen pressure as well as changes in hydrogen concentration has been investigated on sensor properties. The results show that the fabricated sensors have acceptable sensitivity, reversibility, stability and reproducibility at room temperature