Abstract: Sulphidation method for a UO2 powder, in which said powder is sulfurated by bringing it into contact with a gaseous sulphidation agent. Method for manufacturing nuclear fuel pellets based on uranium oxide, or mixed oxide of uranium and plutonium, from a load of totally or partially sulfurated UO2 powder or UO2 powder and PuO2 powder, by lubrication, pelletizing and sintering, in which: the load of powder subjected to the lubrication, pelletizing and sintering is prepared by the following successive steps: sulphidation of a UO2 powder by the above sulphidation method; optionally mixing, said sulfurated powder in a matrix comprising a UO2 powder, or of a UO2 powder and a PuO2 powder; and, subjecting said load, formed from said sulfurated powder or said mixture, to lubrication, pelletizing and sintering operations.