The present invention relates to a method for preparing a lactone. The invention relates in particular to the preparation of butyrolactone, valerolactone and caprolactone. The method for preparing a lactone according to the invention is characterized in that it includes the reduction of a dicarboxylic acid using hydrogen, in the gaseous phase and in the presence of an effective amount of a catalyst including an active ruthenium-tin phase consisting of at least one Ru2Sn3 alloy and an Ru3Sn7 alloy.