A blow mold provided with a locking system for mutually locking each half-mold with the related half-mold holder, thus allowing a simpler and quicker replacement of the side half-impressions of the mold. The blow mold of the invention provides for the side half-impression of each half-mold to be fixed in a cavity of the corresponding mold holder by actuating at least one quick coupling device comprising a bar (23) inserted in one of the two longitudinal edges of the half-mold holder (3) and adapted to move only by rotation about an axis thereof; actuation means (22) adapted to actuate a rotation of said bar; and at least one locking fin (21) fixed along said bar (23) and adapted to move, by rotating the bar (23), from an unlocking position to a locking position in which said locking fin interacts with the respective half-mold (2).