Subthalamic nucleus (STN) has been known to play an important role in the regulation of cortico-basal ganglia-thalamo-cortical loop. STN neurons have pacemaking activitiy and their firing pattern can switch from spike mode to bursting mode when membrane potential becomes hyperpolarized. Recent study has shown that STN neurons show marked increase in burst and oscillatory activity during the dopamine-depleting state of Parkinson's disease (PD). This electrophysiological change in activity is now considered as an characterstic pathophysiological feature of PD. High frequency stimulation of STN can modify and "normalize" the activity of STN neurons in the pathophysiologial state. This electrophysiological treatment applied to STN, known as deep brain stimulation (DBS) clinically, ameliorates the symptoms of PD effectively, and is becoming a standard treatment in patients with advanced PD. This article would review the basic researches concerning electrical activities of STN and try to extend the basic knowledge into clinical applications.