An amphibious foldable treadmill includes: a main frame having at least a wheel rotatably mounted on a base of the main frame to be rolled on a ground floor or on a pool bottom, a tread belt device pivotally secured to the main frame and unfolded from the main frame to be laid on the floor or pool bottom for treading operation, and a hand rail device pivotally secured to the main frame and pivotally connected with the tread belt device, whereby upon folding of the hand rail device and the tread belt device to the main frame, the treadmill can be folded for convenient handling, moving, launching in a pool or landing on the ground floor from the pool for successfully serving as an amphibious treadmill.
