A radio-frequency resonance sensor with variable capacitance for gas/liquid volume ratio measurements is presented. The variable capacitor is made in the form of two semi-cylindrical electrodes, mounted on the outer side of the wall of a dielectric pipeline through which a liquid with gaseous bubbles flows. The variation in the percentage of the gas and liquid causes the capacitance of the electrodes to be changed. Because the electrodes are connected to a resonant circuit of an oscillator tuned to high frequency of 80MHz, the capacitance variations change the frequency of this oscillator. The changes of frequency generated by the oscillator are the measure of the gas and liquid volume ratio of a two-phase flow in the pipe. In the experiments, two half-cylinder electrodes of height of 10mm were mounted on the outside wall of a pipe of diameter of 40mm. The frequency deviations were up to 4MHz when the pipe was empty or filled with water.