The synthesis of methanethiol from H2S-rich syngas was investigated over sulfided Mo-based catalysts supported on SiO2. At CO/H-2/H2S = 1/1/2, 0.2 MPa, 3,000 h(-1), and 300 degrees C, mainly CH3SH, COS, and CO2 were formed, along with small amounts of hydrocarbons and thioethers over potassium-promoted Mo-based catalysts. Studies of the reaction pathway show that COS is a primary product, which is hydrogenated to CH3SH and H2O. Most of CO2 originates from water-gas shift reaction. The hydrocarbons and thioethers originate from the hydrogenation of CH3SH.