The subject of the invention is a method for treating a natural gas containing ethane, comprising the following stages: (a) extraction of at least one part of the ethane from the natural gas; (b) reforming of at least one part of the extracted ethane into a synthesis gas; (c) methanation of the synthesis gas into a methane-rich gas; and (d) mixing of the methane-rich gas with the natural gas. Installation for implementing this method.