The tire-mounted step stool is a step is adapted for use with a tire of a vehicle. When the tire-mounted step stool is secured to the tire, the tire-mounted step stool forms a platform upon which a person can step to gain access to the roof or engine compartment of the vehicle. The tire-mounted step stool comprises a first panel, a second panel, a first steel bar, a second steel bar, and a plurality of hinges. The first steel bar and the second steel bar are used to attach the first panel to the second panel. The plurality of hinges is used to make the stated attachments in such a manner that the tire-mounted step stool is collapsible.