A device for closing zippers on plastic bags, the device being separable from the bags to enable repeated usage. The closing device is adapted to function as an extension of the finger-thumb action. It comprises a generally inverted U-shaped channel for receiving the interlocking elements of the zipper with the opposing legs of the device being resilient and engageable toward one another to press the interlocking zipper elements together. A guide is formed in the legs to align the zipper elements. Projections opposite the guide aid in giving a sense to the user of aligning of the guide with the zipper elements.