A microfluidic device and a method of controlling a fluid included in the microfluidic device. The microfluidic device includes: a chamber; a first fluid that is disposed in the chamber and in which a hygroscopic material is dissolved; a second fluid that is disposed in the chamber and is immiscible with the first fluid; and an electrode portion provide in the chamber and is configured to form an electrical field in the chamber when a voltage is applied to the electrode portion, wherein an interface between the first and second fluids is varied according to the electrical field.