Dimethylmercury (DMM) has been discovered to be one of the organomercury compounds in natural gas, besides mercury metal. The effect of the DMM on the corrosion of carbon steel and aluminium metal was rather frightening, as compared to that of elemental mercury or mercuric chloride, which is well-known as a severely corrosive agent. The results showed that DMM in methanol or petroleum ether as solvent gave similar corrosion patterns to the elemental Hg solution. It revealed uniform characteristics on carbon steel and pitting appearance on aluminium. The higher DMM concentration or the higher reaction temperature, the more severe corrosion occurred because of the higher elemental Hg concentration generated. Trace amount of hydrogen chloride or hydrogen sulfide, which is also present in large quantity in natural gas, remarkably increased the corrosion potential of DMM on metal. Corrosion rate was approximately 700 times faster than the one containing only DMM and 40 times faster than the one containing only acid.