The catalytic oxidation of hydrogen sulfide in the presence of excess water and ammonia on Co3O4/SiO2 catalyst is studied with a fixed hed flow reactor. Hydrogen sulfide was successfully converted to a mixture of elemental sulfur and ammonium thiosulfate (ATS) without considerable emission of sulfur dioxide. A high concentration of hydrogen sulfide and ammonia increases the sulfur production. However, ATS increases with increasing oxygen and water vapor. From the experimental results, complex reaction paths are proposed for the production of elemental sulfur and ATS.