A wearable device includes a main body, a support portion, an electrode assembly, and a processor. The main body can be worn by a user. The support portion is secured to the main body and faces the user. The electrode assembly is secured to the support portion, and includes two electrode arrays and a plurality of carbon nanotubes arranged in arrays. Each electrode array includes arranged electrodes electrically connected to each other. The electrodes of each electrode array include at least two first electrodes each electrically connected to one carbon nanotube. The carbon nanotubes electrically connected to the two electrode arrays are alternatively arranged on the support portion and spaced from each other to form a detecting surface. The processor detects a resistance value of each electrode assembly, and determines an amount of the perspiration corresponding to the detected resistance value.