An electronic device includes a casing, a fan bracket and a fan module. The casing includes a top plate and a bottom plate spaced from and facing the top plate. The fan bracket is mounted on the bottom plate. The fan module includes a fan, a fan holder enclosing the fan therein, and two vibration dampening structures mounted on opposite top and bottom sides of the fan holder. The fan holder is engaged in the fan bracket. The vibration structures protrude beyond the top and bottom sides of the fan holder and abut the top plate and the bottom plate of the casing, respectively.