Hammer disarmer for rifles, constituted of a cylindrical pin lodged in the hammer itself having an operable protruding head over the curved upper surface of the hammer spur, going downwards through a cylindrical portion provided with a frontal plane recess, within which a positioning transverse pin limiting the movements of the disarming axle operates, over which a small return spring lodged within the hole of the hammer also actuates, said hole whose diameter decreases downwards, lodging and guiding the whole elongated portion of the disarmer until its end emerges from the lower plane face of the hammer, where it actuates the disarming lever. If the hammer is armed, a thumb pressure on the actuation head, is sufficient to release the hammer disarmer, which is pushed by the corresponding spring to an interrupted rotation when fitted to the trigger, before the position of percussion. If the hammer is disarmed, it can be simply armed with the thumb to fire the gun, pulling the trigger when desired.