This paper describes the decomposition pathway of methyl mercaptan (MM), a the typical malodorant, and sulfur balance during its decomposition in two systems: (i) an ultraviolet (UV) lamp system and (ii) a sheet material with titanium dioxide supported on fiber activated carbon with UV-irradiation (FAC/TiO2 sheet) system. The observed MM removal rates were found to be higher in the FAC/TiO2 sheet system than the UV lamp system. As decomposition products of MM, dimethyl disulfide, carbon disulfide, sulfur dioxide, methane sulfonic acid, and sulfuric acid were detected in the FAC/TiO2 sheet system, while the same five compounds and hydrogen sulfide were produced in the UV lamp system. These compounds accounted for the sulfur balances in the FAC/TiO2 sheet and the UV lamp systems at 50-79% and 100%, respectively. Finally, the obtained results allowed us to propose MM decomposition pathways in both systems.