In this paper we present a novel unactuated mechanism that utilizes gravity to jump. The passive jumper is a hoop whose center of mass does not coincide with its geometric center. When the hoop rolls down an inclined plane, the center of mass of the hoop moves along a cycloid. As the hoop gains speed moving down the inclined plane, the normal reaction between the hoop and the plane becomes insufficient to ensure contact between the hoop and the plane. This allows the hoop to ‘jump’. Experiments and analysis show that such a jump can be significant, with the jump height from the plane being as high as one body length (diameter) of the hoop. The mechanics of the passive jumping hoop powered by gravity investigated in this paper can inspire the design of actuated jumping robots that can both roll and jump.