Abstract: A bag with a security closure having two opposing main segments corresponding to the bag front panels, and a pair of side segments at each end of the opposing main segments which are foldable about a crease line, the upper edges of the front panel segments and side segments defining the bag mouth. A stiffening bar is provided at the upper edge of each of the main segments and side segments, the stiffening bars being formed in a group when the bag segments are folded to close the bag mouth. There is a closure bar having a U-shape channel with an inwardly extending flange at each end and the group of stiffening bars fits within the inwardly extended flanges of the U-shaped channel as the closure bar is moved over the group of segments with the flanges being below the group of stiffening members. A locking member is fastened to the end of the closure bar to prevent its withdrawal from the bag and a receiver for the locking member can be on a piece that is articulated from the closure bar.