Hydrogen (H2) is a renewable energy source and has many applications such as chemical production, fuel cell technology, fuel for cars, rocket engines, etc. Hydrogen is colorless, odorless, tasteless, flammable and explosive above 4% concentrations in any ambient and cannot be detected by human senses. The detection of hydrogen in a wide range concentration is crucial for l eak detection and safety issue. The resistor based hydrogen sensor could be divided into two parts as metallic resistor and semiconducting metal oxide resistor sensors. Most of the commercial semiconductor hydrogen sensors are still suffering from the slow response, poor selectivity at room temperature. In contrast, metal - based hydrogen sensors, such as Palladium (Pd), exhibit excellent selectivity to hydrogen owing to their high hydrogen solubility and diffusivity. The sensing mechanism of palladium resist ive hydrogen sensor could be explained in two categories: Palladium hydride formation ( increase in resistance) and hydrogen induced lattice expansion (HILE) effect ( decrease in resistance). The research on palladium resistive hydrogen sensor has been focused on to improve the sensor parameters such as sensitivity, selectivity, reversibility, operation temperature, size, response time and recovery time. Different methods such as porous layers have been used to improve the sensing behavior of hydrogen gas sensors. Literature review showed that al though nanofibrous layers, as a substrate for sensors enjoy unique characteristics, but up to now porosity in the substrate of sensors, ha s been formed by anodizing or baking in most cases. In this study, we focus on metallic resistive hydrogen sensor ty pe and it contain palladium layer on polyacrylonitrile nanofibers substrate that is nanoporous and flexible. Therefore, different polyacrylo nitrile nanoporous substrates with random and parallel array were electrospun from 10, 12, and 15 percent (w/v) solutions of polyacrylonitrile. These substrates were coated with 2, 4, and 10 nm of palladium through magnetron sputtering method. Map EDS and GIXRD proved the absence of palladium on the surface of the nanofibers. It was also shown that the coated palladium followed the fiber form. The sensors showed sensitivity to hydrogen gas with a concentration as low as 12 ppm in argon at room temperature. The electrical resistance of the sensors decreased up to 50 ppm concentration of hydrogen and increased from concentrations of 125 ppm upwards. Hence it is concluded that up to 50 ppm concentration, the ruling mechanism follows hydrogen induced lattice exp ansion and with concentrations of 125 ppm and higher, the palladium hydride formation mechanism rules. The sensitivity of the sensors increased with increasing nanofiber diameter for equal palladium thicknesses, but the response time did not show much diff erence with increasing nanofiber diameter. With constant diameter of nanofibers, sensitivity and response time of the sensors increased. The sensors with randomly arrayed nanofibers of 104 nm and 140 nm diameter, coated with 4 nm of palladium showed well d efined behavior. It was also shown that sensors with randomly arrayed nanofibrous substrate had a higher sensitivity as well as lower response time in comparison to film, glass and randomly arrayed fibrous substrate. Moreover, the FESEM, and FTIR analysis showed no considerable change in the morphology and chemistry of nanofibers before, after coating with palladium as well as after exposing to hydrogen