The present disclosure provides a height-adjustable cup holder. The cup holder includes a cup holder housing including a first stand and a second stand, which are positioned adjacent to each other, a guide member positioned on a bottom surface of the cup holder housing between the first stand and the second stand, a cup holder unit, which includes a first cup holder plate, a second cup holder plate, and a central member, which is positioned between the first cup holder plate and the second cup holder plate and is fitted onto the guide member, the cup holder unit being releasably coupled to the cup holder housing, and first and second support plates, which are moved along the respective cup holder plates so as to hold the cup holder unit on an inner side surface of the cup holder housing.