Disclosed are a rotor plate and a rotor assembly including the same. The rotor plate includes a plate body including a first part having a first hole at a center, and a second part having a second hole at a center, the second part having a diameter corresponding to the first part, and connected to the first part in a first direction that is an axial direction perpendicular to the first part, and a diameter of the second hole is larger than a diameter of the first hole, a first slot recessed on an outer peripheral surface of the plate body, a second slot recessed on the outer peripheral surface of the plate body, and a first plate passage formed on a wall of the first part in the second direction that is opposite to the first direction, and connecting the first slot and the first hole.