A grease cover (50) for protecting grease spread on a bottom surface of a heat sink (20) includes a base wall (51), a plurality of sidewalls (52a, 52b, 52c, 52d), a protecting space (53) between the base wall and the sidewalls, a holding space in an upper portion of the protecting space, and two projections (54). The protecting space is for accommodating the grease. The holding space is for receiving the heat sink therein. The projections extend from two opposite sidewalls of the grease cover. A top surface of each of the projections spaces a distance from the base wall, for supporting the bottom surface of the heat sink to enable the grease away from the base wall, when the heat sink is received in the holding space.