In this study, the hybrid reactor has been used to remove H₂S from the toxic gas. Since the oxidation and reduction reactors were combined, their sizes were important to stabilize developed process. The optimal sizes of oxidation and reduction reactors were determined considering iron oxidation rate and H₂S removal rate. The optimal ratio of reactor size was 4 L for oxidation reactor to 1 L for reduction reactor. Immobilized Thiobacillus ferrooxidans has been developed to minimize the size of oxidation reactor. Since the immobilized cell enhanced the oxidation rate, it was possible to increase H₂S removal efficiency. It was possible to increase operation time because immobilized cell can survive longer than free cell.