The invention relates to a method for the removal of mercury from gas containing sulphur dioxide and oxygen and from the sulphuric acid vapour contained in the gas. According to the method, the gas is washed with a water solution that contains selenium ions, whereby metallic selenium is formed in the presence of oxygen, which precipitates the mercury in the gas and vapour either as a selenide or in a chlorine-containing environment, as a dichloride of mercury and selenium. Gas washing occurs at a low temperature, below 50.degree. C.