The behavior of mercury in a multicomponent slurry gasifier (MCSG) is investigated in this work. An industrial scale MCSG for ammonia production operated at 1300-1400 degrees C and 1.0-1.6 MPa is used for the study. The effects of waste cogasification and redox condition of the process water are explored. The redox condition is found to be an important factor in determining Hg distribution in the MCSG output steams. Hg is mainly distributed to the clarified water (81.6-93.2%) in the tests with oxidizing water conditions. However, Hg primarily partitions into the raw syngas (82.5-99.2%) for the tests with reducing water conditions. Compared with gasification of coal only, Hg in the raw syngas from cogasification of waste with coal is slightly increased, even though the Hg level in the waste is generally high. An increase in the oxygen content in the process water is beneficial for Hg capture in the water and in the solid stream. The process water contributes 64.5-100.0% of the total Hg in MCSG when water recycling is employed. Attention should be paid to Hg removal in the process water.