Methylmercaptan (MM) gas was continuously treated in four systems: (i) an ultraviolet (UV) lamp system, (ii) a sheet material with titanium dioxide supported on fiber-activated carbon (FAC/TiO2 sheet) with UV-irradiation system, (iii) a FAC/TiO2 sheet system, and (iv) a sheet material with titanium dioxide supported on fiber without activated carbon (TiO2 sheet) with UV-irradiation system, in order to clarify the sulfur balance and the effects of fluctuation of MM load in the continuous treatment of MM using photocatalyst supported on FAC. The sulfur balance in each system was accounted for by MM, dimethyl disulfide (DMDS), sulfur dioxide, and methane sulfonic acid. Although approximately 100% of MM was removed in the UV, FAC/TiO2/UV, and TiO2/UV systems, there were differences in the production of DMDS, a malodor compound. As the concentration of MM in the inlet gas increased, the production ratio of DMDS in the UV and TiO2/UV systems became higher than in the FAC/TiO2/UV system. These results indicate that the FAC/TiO2/UV system has a higher capacity to deodorize MM than the UV and TiO2/UV systems.