Abstract: The invention features a method for treating a supported catalyst with a sulphur compound based active phase and a mercury compound contaminated mineral support. This method consists in implementing the following steps: the said catalyst is contacted with a basic aqueous solution of at least one sulphide selected among alkaline metal sulphides, alkaline-earth metal sulphides or ammonium sulphide; then the catalyst is separated from the basic aqueous solution. At the end of this process, the treated catalyst shows the same characteristics as before its contamination by mercury.