Abstract: A plastic zipper including a male hook and a pair of female hooks that are engaged with each other to form a combination thereof. In the plastic zipper, when an opening force is applied to the plastic zipper from an opening side thereof, the pair of female hooks is provided on a flange, a portion of which, being defined by base portions of two female hooks on an opening and content side, becomes flexible. The plastic zipper is favorably used for containers for packaging, since it permits resistance to opening on the opening side to consistently hold a low value of from about 0.9 kg/5 cm to about 1.