An enclosure of an electronic device includes a chassis, a sliding plate slidably disposed on the chassis, and a pivot member. A number of vent holes and a location hole are defined in the chassis. A number of teeth are formed on a sidewall bounding the location hole. A through slot is defined in the sliding plate. A toothed rack is formed on a sidewall bounding the through slot. The pivot member extends through the through slot and the location hole. The pivot member includes a toothed portion engaging with the toothed rack and the teeth, and a smooth neck. When the toothed portion disengages from the teeth, the neck is pivotably received in the location hole, the pivot member is pivoted to drive the sliding member to slide relative to the chassis by the toothed portion rolling on the toothed rack, thereby exposing or covering the vent holes.