In this work, molybdenum trioxide (MoO₃) was synthesized and deposited on tapered optical fiber using the drop-casting technique for hydrogen (H₂) detection at room temperature. A transducing platform in a transmission mode was constructed using multimode optical fiber (MMF) with a 125 µm cladding and a 62.5 µm core diameter. To enhance the evanescent light field surrounding the fiber, the fibers were tapered from 125 µm in diameter to 20 µm in diameter with a 10 mm waist. The microstructures and chemical compositions of the fabricated sensor were analyzed by field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX), differential X-ray (XRD), and atomic force microscopy (AFM). In addition, the gas detection properties of the fabricated sensor were studied by exposing it to various concentrations of hydrogen gas from 0.125% to 2.00%. As a result, the sensitivity, response, and recovery time were 11.96 vol%, 220 s, and 200 s, respectively. Overall, the fabricated sensor exhibits good sensitivity as well as repeatability and stability for hydrogen gas detection.