There is disclosed a slider for a plastic zipper, including an inside guide which is inserted between a pair of male hook and female hook of a plastic zipper, functions so as to disengage the male hook and female hook from each other by the sliding movement of the slider, is installed on the slider main body rotatably about an axis perpendicular to the plastic zipper, and is capable by the rotation, of being located at a prescribed position where it functions as such or being dislocated from the above prescribed position.The above slider is easily attachable to a plastic zipper at a rate higher than a bag manufacturing rate, and is prevented from falling-off even if a small plastic zipper is formed of a thin film with low strength.