Abstract: The present invention relates to a method for chemo-mechanical cleaning of the barrel of a gun, in which method the barrel is closed tightly from both ends and at least one cleaning chemical is introduced into the closed barrel, the chemical is allowed to react with the impurities on the interior surface of the barrel, the chemically treated residue is loosened mechanically, the residue is removed from the barrel and, if necessary, the barrel is rinsed and dried. According to the invention, at least one of the cleaning chemicals used is a gaseous cleaning chemical. The invention also relates to a device for cleaning the barrel of a gun, comprising end blocks (1,8) sealably fittable to each end of the barrel and a reciprocable mechanical cleaning element to be placed in the barrel.