A foldable humidifier (100), comprising a fixed base (10), a foldable storage cup (20) for accommodating liquid, and a humidifier assembly (30). A lower end of the foldable storage cup (20) is sleeved and fixed on the fixed base (10); the humidifier assembly (30) comprises an upper cover (31), a one-way floating ball (324) valve (32), a water level probe (33), a water absorbing cotton (34), a driving circuit board (35), an atomizing sheet (36), and a battery (37); the upper cover (31) is fixedly provided above the foldable storage cup (20); the one-way floating ball (324) valve (32), the water level probe (33), the water absorbing cotton (34), the driving circuit board (35), the atomizing sheet (36), and the battery (37) are all fixed to the upper cover (31); a one-way floating ball (324) valve (32) air inlet and one end of the water level probe (33) are located in the foldable storage cup (20); the other end of the water level probe (33) is connected to the driving circuit board (35); the driving circuit board (35) is connected to the atomizing sheet (36); the other end of the water absorbing cotton (34) is in contact with the atomizing sheet (36); the battery (37) is connected to the driving circuit board (35). The foldable humidifier (100) can be folded according to the water level, and is convenient to carry; by adoption of the water absorbing cotton, the foldable humidifier is easy to clean, and the service life is prolonged.