A foldable bicycle has a frame unit and a positioning unit. The frame unit includes a front wheel unit disposed on a front frame rod, a rear wheel unit disposed on a rear frame rod and aligned with the front wheel unit along a longitudinal direction of the bicycle, and a horizontal pivot pin interconnecting the front and rear frame rods rotatably such that the pivot pin and rotating axes of the front and rear wheel units forming generally an isosceles triangle. The positioning unit positions the rear frame rod behind the front frame rod, and is operable to allow for rotation of the front and rear frame rods about the pivot pin so as to dispose the bicycle at a folded position, where the front and rear wheel units are aligned with each other along a transverse direction of the bicycle.