A magnet case for a rotor includes a hollow cylindrical supporting body for accommodating two magnetic bands, an annular flange extending outwardly from a top end of the supporting body, and a positioning plate extending inwardly from a bottom end of the supporting body. The annular flange of the magnet case has two spaced notches defined in an outer periphery thereof, and the two spaced notches are configured to reduce vibration of a cooling fan associated with the rotor during operation of the cooling fan. A rotor incorporating the magnet case is also provided.