A ski boot comprising a lower part or shell, suitable for enclosing the user's foot and an upper part or cuff, suitable for enclosing the lower part of the skier's leg, wherein the cuff is hinged to the shell so as to rotate relative to the shell around hinges defining a rotation axis, forward, toward a tip of the boot, and backwards toward a heel of the boot, wherein the boot comprises fastening means suitable for selectively locking and/or unlocking the rotation of the cuff with respect to the shell depending on whether the user wants to switch from a skiing configuration to a walking configuration, respectively. Advantageously the fastening means comprise a slider interposed between the cuff and the shell, wherein said slider is fixed in rotation to the cuff and it comprises first and second end stops, placed at opposite sides of the slider, wherein the slider is movable in translation with respect to the cuff in order to move from the unlock or walking configuration, wherein the first and second end stops do not interfere with the rotation of the cuff with respect to the shell, to the lock or ski configuration wherein the first and second end stops abut against respective first and second abutment of the shell, wherein first abutment blocks the forward rotation of the cuff with respect to the shell and second abutment blocks the backward rotation of the cuff with respect to the shell.