A kick scooter includes a deck, an upright tube, and a folding mechanism. The upright tube is mounted by the folding mechanism to the deck. The folding mechanism includes a mounting case mounted on the deck and two connecting arms attached to the upright tube. The mounting case is pivotally mounted to a rocking arm that is provided with a position-restoring preloading force and has a free end to which a moving bar is attached. The two connecting arms are respectively formed with arc guide slots opposite to each other and centered at a pivotal joint to receive a moving bar of the rocking arm to extend therethrough for being guided thereby to move. Each arc guide slot has two ends respectively formed with a folding positioning notch and an expanding positioning notch for selectively positioning the moving bar therein as being biased by the position-restoring preloading force.