A wireless sensing device disposed a drum along with laundry to measure humidity in the drum, thereby increasing accuracy in estimation of a degree of dryness, a dryer for determining a degree of dryness of the laundry using the wireless sensing device, and a method of controlling the dryer. The wireless sensing device includes a sensing module including a humidity sensor for measuring humidity in a drum of a dryer into which the wireless sensing module is thrown; a sensor communication module transmitting or receiving data with a main communication module of the dryer through wireless communication; a sensor controller configured to control the sensor communication module to transmit a humidity value corresponding to an output of the sensing module to the main communication module; and a sensor power supplier supplying power to the sensing module, the sensor communication module, and the sensor controller.