A mounting device capable of mounting two objects of different sizes is disclosed. The mounting device includes a mounting member including a first end, a second end opposite to the first end, a mounting portion, a securing piece between the first end and the second end, and an installing plate including a first installing portion and a second installing portion. The mounting member is secured to the first installing portion and the second installing portion. When the mounting portion and the securing piece are engaged with the first installing portion, the first end is adapted to abut a first object. When the mounting portion and the installing portion are engaged with the second installing portion, the second end is adapted to abut a second object of a different size from a size of the first object.