WO₃ nanonodule-decorated carbon nanofibers (CNFs) of various diameters were fabricated by single-nozzle co-electrospinning using two phase-separated polymer solutions. Using more polyvinylpyrrolidone (PVP) solution decreased the CNF diameter from 130 to 40 nm and increased the Brunauer–Emmett–Teller (BET) surface area from 147 to 276 m² g⁻¹. A spin-coating method was used to deposit the hybrid CNFs on the sensor substrate to minimize the contact resistance between them. In addition, ultraviolet (UV) irradiation lowered the desorption energy level of the NO₂ gas between the transducer materials during the recovery time. As a result, the recovery time decreased to ca. 7 min using UV light with an intensity of 75 mW cm⁻². The sensitivity of the hybrid CNF gas sensors increased with decreasing diameter of the CNFs; the minimum detectable level (MDL) was 1 ppm at room temperature for 40 nm hybrid CNFs dispersed uniformly on the electrode. Furthermore, increasing the amount of decorated WO₃ nanonodules on the CNF surface enhanced the sensitivity to NO₂ gas. The NO₂ sensor made with the hybrid CNFs had sensing performance comparable to those made with conventional metal oxide-based nanomaterials and pristine carbon nanotubes (CNTs).