A solid-state compact potentiometric hydrogen gas sensor was developed using CH3COONH4-doped chitosan as polymer electrolyte. The 40 wt% CH3COONH4-doped chitosan was used as the electrolyte in the sensor. The X-ray diffraction and the scanning electron microscope results showed that the nano-sized platinum working electrode and silver reference electrode were deposited on the respective side of polymer electrolyte by the impregnation-reduction method. The generated electromotive force increased linearly with the logarithm of hydrogen concentration at room temperature. Either insufficient or excessive impregnating time works against the gas sensitivity, and the polymer electrolyte prepared by impregnating 5 min endows the sensor with the best hydrogen-sensitive performance.