A transformable bag includes a first storage unit and a second storage unit connected with each other, and a third storage unit disposed between the first storage unit and the second storage unit. The first storage unit and the second storage unit are respectively connected to two side edges of the third storage unit by two connecting units. When the first storage unit and the second storage unit are away from each other, the third storage unit is stretched to form a placing space for an infant to rest or changing diapers. When the first storage unit and the second storage unit are close to each other, the third storage unit is stored between the first storage unit and the second storage unit, and the third storage unit can be removed to release a storage space between the first storage unit and the second storage unit.