A process for the synthesis of (per)fluorinated mono-functional carbonyl compounds having the following formula: F—A—(RF)t—B—C(O)X1  (I) wherein: X1=F, CF3; t=0, 1; A, B equal to or different from each other, are independently C1-C5 (per)fluoroalkylene groups or C1-C5 (per)fluorooxy-alkylene groups; RF is —Rf1—, C1-C20 perfluoroalkylene, —ORf1O—; or —ORf2—, wherein Rf2 is a perfluorooxyalkylene chain; wherein the carbonyl groups of a (per)fluorinated di-functional carbonyl compound of formula (III): X2(O)C—A—(RF)t—B—C(O)X1  (III) wherein: X1, RF, t, A and B have the above meanings; X2, equal to or different from X1, has the same meanings as X1; are partially fluorinated with elemental fluorine in the presence of a catalyst having formula MeFy.zHF, Me being an alkaline or alkaline-earth metal or Ag, y=1 or 2, z an integer from 0 to 4, carrying out said reaction at a temperature higher than a temperature such that it leads to the formation of C(O)FX2.