Abstract: An expandable mattress cover comprises a top sheet, a bottom sheet and a side wall joining the top sheet and the bottom sheet. A plurality of edges of the side wall is stitched to the top sheet and the bottom sheet to form a compartment. An expandable means having a hook is attached to the side wall. An opening is provided on the side wall for inserting a mattress into the compartment. The expandable means may be adjusted to fit mattresses of different thicknesses inside the expandable mattress cover. A fastening means with a hook is adjusted to open the opening before inserting a mattress into the compartment. The mattress is secured in position by adjusting the fastening means to a closed position. The hook is used to clip the expandable means and the fastening means onto the side wall.