A bracelet clasp including an easily manipulated device of simple structure for adjusting the usable length of the bracelet by a firm adjustment, including when the clasp is open. The adjusting device is separate from the locking member, and the lock is arranged to move from its closed state to its open state by the user acting on the control member of the locking member such that the adjusting device is capable of being shifted independently of the open or closed state of the clasp. The clasp has a discrete structure, since it is actuated by the control member already provided for unlocking the clasp, although it is separate from the locking member of the clasp, and this additionally allows the length of the bracelet to be adjusted even when the clasp is in its closed state.