Abstract: A method for non-invasively measuring the impedance of a plasma discharge. Parallel anode and cathode electrodes are connected to a DC voltage source that ignites and sustains a plasma between the anode and cathode. A network analyzer applies a frequency-swept AC signal superimposed onto the DC voltage applied to the electrodes. The voltage of the AC signal reflected by the plasma is measured by the network analyzer through one of the electrodes used to sustain the plasma and is used to find the complex impedance of the plasma as a function of the applied AC frequency. Since the electrode serves dual purposes, the insertion of an additional physical probe that could introduce perturbations or contaminate the discharge is not necessary.